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Air Conditioning and Heat Pump Troubleshooting Simplified

troubleshooting air condtioners and heat pumps

This page contains a list of Air Conditioning problems and parts that I use to repair the problems. I see these problems most often every summer in our 27 year old HVAC business. Let us help you repair your air conditioner and save money! If you have any questions I will be happy to try and answer them. Please feel free to email us anytime:

Let us Help You Repair your Air Conditioning System and Save Money!

*Summer Air Conditioning Tips:

1. Always turn your air conditioning system off if there is a threat of a storm. A lightning power surge, or if the power is goes off and on can ruin your air conditioning system. We get lots of repair calls after a storm. These calls could be prevented if people could remember to turn their air conditioners off during a storm.

2. I would like to suggest keeping an extra capacitor on hand. I see lots of capacitors go out during the hot summer months. We sell capacitors on the following page: Please click here to see the capacitors we sell.

  3. If your outdoor air conditioning unit is not coming on at all, then we would suggest that you first check the circuit breaker to make sure the breaker has not tripped. Even if the breaker does not look like it is tripped. Flip the breaker completely off then back on. This is the first question we ask a customer when we receive a service call and the customer says the outside unit is not coming on. “Have you checked your circuit breaker?” Many times we have gone to homes where the breaker was the only problem. This simple circuit breaker check could save you an expensive service call. *When resetting a circuit breaker always only touch the plastic handle of the breaker with one hand. Do not ground yourself out to the breaker box or touch any other metal when resetting the breaker. Always wear shoes. You do not want to be grounded to the box in case the compressor has ground out.   Below are listed the parts that I see go out most often. We even have one device that will help start your compressor if it is locked up called “Super Boost!” Please click here if you are interested in seeing the Compressor Super Boost.

Listed below are many of the air conditioning problems that I see on a daily basis in our heating and air conditioning business here in Louisville, Kentucky. I wanted to list some of the problems and give you links to the parts so you can repair your air conditioner.

Please see the section near the bottom of this page, “What to Check for If Your Air Conditioning System is not Working.” I try to give step-by-step procedures on how to troubleshoot your air conditioning system.

Please click on the link if you would like to see an air conditioning troubleshooting flow chart. This should help you troubleshoot to see what is wrong with your air conditioner. Please click on your browsers back “<” button to return to our site. Please click this link if you would like to download the air conditioner troubleshooting flow chart.


One of our customers suggested the PDF so you can print it out and take it to your air conditioner for easier troubleshooting. We would love to have your business!

***Please Always, make sure all electrical power is turned off before attempting to do any heating or air conditioning repairs.

We have a real good testing meter for sale on the following page: Click here: UEI G2 Phoenix Pro #DL379 Multi Function Digital Multimeter

Problem #1: Outdoor condensing fan motor has stopped running. This problem could be caused by a bad motor run capacitor. Please see our Run Capacitor Page to purchase a new capacitor. Here is a link to our capacitor page: Please click here to see the capacitors we sell. If you do not have a capacitor tester you may want to take you capacitor to your local appliance parts supplier and see it they will test the capacitor for you. We sell a real good capacitor tester on the following page. Please click here if you are interested in a capacitor testerIf your motor capacitor is not the problem, then more than likely you need a new motor. Is the fan blade tight, stiff or hard to turn? If the fan blade is hard to turn then you probably need a new motor because the motor bearings are messed up. Please click here if you are interested in the condenser fan motors we sell. Please send us your unit’s model number if you would like us to use our online parts programs to look up and see which motor your unit uses. Our email address is:

Problem #2: Air conditioner compressor will not start. When power is applied to the air conditioning outdoor unit the fan starts, but you hear a sound like the compressor is trying to start, “UGGG”…, for about 5 to 10 seconds and then all you hear is the outdoor condenser fan run. The compressor is locked and will not start. What is happening is the compressor is trying to start, but because the compressor motor is locked it tries to start for a few seconds and then because of the high amperage being drawn goes off on internal overload. The internal overload protects the compressor windings from overheating and burning up. I see this many times during the start of the air conditioning season. Some compressors just have a hard time starting after sitting all winter long. Some compressors are locked up so bad that I can not start (unlock) them and I must tell my customer that they need a new compressor or new air conditioning system. Many times I can get the compressor started again without having to buy a new compressor or new air conditioning system by using the device that I sell below. It is called, “Super-Boost.” I keep two or three of these on the truck. They have saved many of my customers from having to buy new air conditioning systems. Below is a description of the “Super Boost”. Please click here if you are interested in seeing the compressor super boost that I recommend.

The Super-Boost could save you from having to purchase a new air conditioning compressor or system!

The Supco, Super-Boost has the following features that make it a life saver when it comes to air conditioning repair:

  • The Supco can save stuck compressor by increasing the compressor’s starting torque by 500%.

  • The Supco, Super-Boost is a solid state relay and hard start capacitor no loose parts or complicated wiring. Just wire it across your run capacitor as shown below:

On a single capacitor connect as in the picture below. On dual capacitor systems just connect between the “C” and “Herm” terminals.


More Features:


Supco SPP6 Super Compressor Boost Hard Start Capacitor.

Problem #3: This problem is probably the second most common problem that I see every summer. The problem is a bad compressor or fan run capacitor. The Air conditioner outdoor unit will not come on. Either the outdoor fan does not run, the compressor does not run, or both the fan and the compressor do not run. You checked and reset your breaker and the outdoor unit still does not come on. You can hear a little humming sound, sometimes a “Uggg” inside the unit when power is applied. The “Uggg” is the compressor trying to start. You might hear the low voltage contactor humming. You pull the disconnect and disconnect the power to your outdoor air conditioning unit. Please make sure your electrical power is off before working on any air conditioning equipment.You take the door or cover off your outdoor unit’s control box and find a bad, swollen run capacitor. EPA stopped allowing manufacturers to produce capacitors with cancer causing PCB’s. Since they stopped allowing the use of PCB’s the capacitors now have a shelf life. Many times I see capacitor problems that will not allow the compressor or the fan to come on. Many times you can clearly see that the capacitor is bad because it is swollen or even blown apart with capacitor oil everywhere! Sometimes you will need a special meter to test the microfarad (MFD) or (uf) rating. “MFD” and “uf” mean the same. Some capacitors will have “MFD” on them and some will use “uf”. Most of the time you can tell the capacitor is bad because it is swollen up. Please see the picture below for the comparison between a good and bad dual run capacitor. Capacitors are called “Dual” capacitors because the capacitor helps run both the fan and the compressor and it will have three terminals on top labeled: Herm, Com and Fan. Single capacitors will only have two terminals on top. If you have any questions please feel free to email us at:


Bad round dual capacitor on left. Good round capacitor on right.


Bad oval capacitor on the left. Good oval capacitor on right.

Solution: You need to purchase a new capacitor. We have many different types of capacitors listed on our Run Capacitors page. Please click on the following link if you would like to visit our run capacitors page: Please click here to see the capacitors we sell.

We would love to help you out and have your business!

There are so many different types and sizes of capacitors that we have them listed on another page. We will be adding more capacitors as time goes on. Here is a link to our Capacitor Page with an opportunity to purchase Capacitors: Please click here to see the capacitors we sell.

Contactor Problems:

Please Click here to see the contactors we sell.  If you would like to see a You Tube Video on how to change a contactor out then please click on the following link: Please click here to see How to change a contactor.

Problem #4: Air Conditioning outdoor condensing unit or heat pump unit will not shut off. It continues to run no matter what you do. The only way you can get the outdoor unit to shut off is turn off the breaker or pull the outdoor disconnect. Also, sometimes when the contactor fails the outdoor condensing unit will not come on at all. Dirt or insects (I see ants many times) can get in between the contact points while the contactor is off, and cause the air conditioner not to come on at all. If the contact points are pitted and burnt they might now supply enough voltage for the compressor and fan to run. If your contactor has burnt or pitted contacts it is a good idea to replace the contactor. When the contactor is stuck in the “On” position (contacts welded together), Ice will form on the indoor evaporator coil and all the way out to the outdoor unit. I have seen 1 or 2 inches of ice form on the line set and outdoor unit compressor. You will not get hardly any air flow through your duct work when this happens because the evaporator has become a complete block of ice. If this is your problem then your contactor points could be stuck, welded together causing the outdoor unit to run continuously. Many times when ants or insects get between the contactor points the outdoor unit will run (burns the insect out), but because of the uneven wear (arcing) in the contact points the contactor will soon fail. Arcing causes a tremendous heat build up and pitting of the contact points. If you are in an area of the country where insects are prominent in and around air conditions, then I would suggest you blow your contactor out with compressed air or check and make sure you do not have any insects in between the contactor points at the beginning of each cooling season. You might want to keep a spare contactor on hand?

If your contactor looks like the single pole contactor below, with burnt or pitted contacts then you need a new contactor. The picture below is a single pole contactor out of a Rheem, Ruud air conditioner.

burnt contactor

Solution: You need to solve this problem by purchasing a new contactor. We sell contactors on the following page: Please Click here to see the contactors we sell

Contactor’s Purpose: The contactor has a 24 volt relay, when this 24 volt relay is energized from the thermostat, a call for cooling, the contacts on the contactor close, making a high voltage (220-240) connection to your compressor and outdoor fan, causing the outdoor unit to come on. There are several types of contactors that we sell. They are sold on the following page: Please Click here to see the contactors we sell

**Please make sure your electrical power is off before attempting to remove or work on air conditioning equipment. Before changing out a contactor or working on an air conditioner please make sure you pull the outdoor disconnect or indoor breaker that controls the air conditioner. Turn the furnace off or thermostat off so no low voltage is going through the low voltage wiring.

Term-Lok Compressor Terminal Repair Kit Model TLC-3-10:

Problem #5: Compressor will not run. First, you turn off the power to the air conditioning system. Second you remove the compressor terminal cover and find that one or two of the compressor terminals have burned completely off. Yes! that is why the compressor is not running!

Solution: Remove the old burnt terminal/terminals, and use the “Term-Lok” compressor terminal repair kit to replace the burnt terminals and wires.

The “Term-Lok” compressor terminal repair kit is one of my favorite items to have on the truck during the summer time. The “Term-Lok” compressor terminal repair kit has saved many of my customers from having to purchase new compressors or air conditioning systems. I see many, many burnt compressor terminals during the course of the summer. Many contractors will tell their customers, “You need a new compressor or new air conditioning unit.” Most of the time this is not true! All you need to do is use the “Term-Lok” kit to repair the compressor terminals and you are back in business for a long, long time. Before I found out about the “Term Lok” compressor terminal repair kit I would try to solder the terminals on using a soldering gun. I found out the hard way that the solder would not hold but for a short period of time. Before long, I would get a call again, “My air conditioner is not working.” I would go look at the compressor terminals, and there again, one of the terminals or terminal was burnt completely off again. I could not believe it! Since I have started using the “Term-Lok” repair kit, I have not had one call back for burnt compressor terminals! This new Term-Lok compressor terminal repair kit is not cheap, but it is much better than having to get a new compressor or air conditioning system. This compressor terminal kit costs $40.00. I figure the kit is so expensive because of the brass terminal connectors and the way they have permanently connected the #10 gauge wires. What I really like about this kit is that it lasts! No more burnt compressor terminals! The kit is called “Term-Lok” because it actually locks the wires to each compressor terminal. You use a small Allen key wrench to tighten or lock the solid brass terminals to the compressor terminal stubs. There is an Allen screw that can be placed in either the bottom or top of the brass terminal. This makes the installation easy. If there is 1/4 inch left on the compressor terminal studs, then you can use the terminal lock kit to fix your compressor. Be prepared for the hot summer and have a compressor “Term-Lok” terminal repair kit on hand. Please click on this link if you are interested in the Term-Lok compressor terminal repair kit.


Above is a Close-up of the three brass terminals with Allen wrench and screws.


Above is a picture of the entire kit. The wires are 36″ long #10 Gauge wire

Term-Lok Compressor Terminal Repair Kit Model TLC-3-10 


Above is a picture taken of the label:

Below is a picture of the Installation Instructions.


Please click here if you are interested in the Term-Lok Compressor Terminal Repair Kit Model TLC-3-10 

International Refrigeration Products Low Voltage Universal Transformer #TFM4031:

Problem #6: Nothing works on your heating & air conditioning system. The fan will not blow in the fan “ON” position. The gas burners will not light, the outdoor air conditioning unit will not come on.

Solution: Use a Volt Ohm meter, set the meter to “Volts AC,” to check and see if you are getting between 24-28 volts between your “C” and “R” terminals on your low voltage board, or between “R” the red low voltage thermostat wire and ground. You might have to tape the blower door safety switch, to keep the voltage on so you can perform this test. Turn your power back OFF after completing this test using the Volt meter. Check for fuses on the furnace control board to see if the furnace has a low voltage protection fuse. If the furnace has a fuse pull the fuse out and see if it is blown. If the fuse is blown check all your low voltage wiring to make sure it is not grounding out anywhere. I have seen pinched wires that are stuck between furnace doors, animals that have chewed through wires and just weathered low voltage wiring that has lost its insulation due to the hot sun over the years. Any wires that are touching together can cause the low voltage fuse to blow. The fuse protects the expensive furnace control board from getting burned up because of a short to ground. If the fuse is blown then I would go to the local hardware and purchase 5 to 6 new fuses. If you do not find the problem that is causing the fuse to blow right away then you will need more than one fuse for testing. If your fuse is OK or your furnace does not have a fuse, and you are not getting low voltage between the “C” and “R” terminals then you might need a low voltage transformer. I have seen some of the transformers just go bad. Below I explain the job of a transformer. Please click on the following link if you are interested in seeing the TRM4031 universal transformer.

What is a Low Voltage Transformer? The job of a low voltage transformer is to take 110 volts AC on the primary end, and transform or lower the voltage to 24 volts on the secondary end. That is why on the transformer label, below it has “PRI” 120, 208, 240 and SEC 24V 40VA. The transformer that we sell can be used with multiple voltages either 120 volts, 208 volts or 240 volts. You would hook up the right color coded wire to use the voltage that you have. The color coded voltage wiring directions are on top of the transformer. For example: The white and black wires would be used for 120 volts for most furnaces. The White and Orange wire would be hooked up if you were using the transformer to replace a bad transformer on an outdoor air conditioner or heat pump that uses 240 volts.


Transformer all

Please click on the following link if you are interested in seeing the TRM4031 universal transformer.

Prevent Your Air Conditioner or Heat Pump from Cycling Off and On too much with a

Delay On Make Timer. Beacon Model TDOM:

This Beacon Delay on make timer replaces the following timers: ICM102B, EAC700, EAC701, TD69, 3310-06, 3239, 32367, IC-310, IC-213, & AC-800.

Problem #7- You might consider purchasing and installing the following device if:

1. You have to reset your air conditioning circuit breaker often.

2. If you have electrical storms where the power is going off and on. I

have many calls after electrical storms. Please always turn your air

conditioner off during a storm.

3. If the power goes off and on often in your home. If the power goes off

and on often in your home then this can ruin a compressor. When your

air conditioner is turned off you should wait at least 3 to 5 minutes

before you turn it back on. If you do not wait the 3 to 5 minutes then

this causes a tremendous strain on the compressor motor because the

motor is trying to start without the pressures being equalized. Please

give your compressor and air conditioning system time for the pressures

to equalize before starting your air conditioner again.

4. If you have children living in your home, renters, or other people who

do not understand that you should wait 3 to 5 minutes before cycling

and air conditioner off and on.

Solution: Purchase a delay on make timer pictured below. You can set this timer to the length of time you want to wait for the air conditioner to come back on from .03 of a second to 10 minutes. What this timer does is delay the amount of time you want your air conditioner to come on when low voltage power is applied to the timer. This low voltage timer is simple to install. *Some of the new thermostats have this delay feature built into them. If you have a thermostat that has this delay feature, then you do not need to purchase the Delay On Make Timer pictured below. If you want to protect your air conditioning system from short cycling and possible compressor damage, then the Delay on Make timer is for you! Please remember to turn off all power when working on air conditioning equipment.

Please click on the following link if you are interested in seeing the TDOM, Time Delay On Make relay.

tdom all   tdomclose


Below we have thumbnail pictures with installation instructions and wiring diagram:



Delay On Make Timer Beacon Model TDOM

Prevent Refrigerant Leaks With A

Box of 10 Model #JB NFT5-4 Quick Seal Schrader Valve Caps:

Please click on the following link if you are interested in the JB Quick Seal Schrader Valve Caps.


EasySeal can save you expensive air conditioning repairs! If you have a leak in your air conditioning system EasySeal can inexpensively repair leaks in your system!

Please click here if you are interested in the EasySeal Air Conditioner Leak repair kit.

Problem #8 Air conditioner is freezing up. You see frost or ice on the suction line (black insulated line) Any areas that are not insulated are covered with ice. You are not getting hardly any air flow out of your registers. Your evaporator coil is iced up completely. Most of the time this is caused by being low on refrigerant charge. There are other causes such as:

1. Dirty air filter or some air flow restriction.

2. Dirty blower

3. Slow or dragging blower motor (might need a new capacitor).

4. Dirty stopped up Evaporator coil (Need to have HVAC tech clean coil)

5. Long Air conditioning run times. Setting thermostat below 72 degrees

with cool outside conditions.

6. A stuck contactor that keeps the outdoor unit running even when the

indoor blower is not running or when the thermostat is calling for

cooling. We sell contactors above.

Most of the time a freeze up condition is caused by a low refrigerant charge. Since the air conditioning system is supposed to be a leak free, sealed system this means you have a leak somewhere. I use the Schrader valve caps sold below to make sure that I do not have a leak in the Schrader valves when I take my manifold gauges off. I install these Schrader caps for insurance, because I have seen leaks in these valves many times. These caps have a rubber seal inside of them and insure a leak proof seal.

Below are some pictures with links to the page where you have an option to purchase:


Above, Schrader Caps Installed on an outdoor AC unit.
Above, Schrader Caps Installed on an outdoor AC unit.

Above, Schrader Caps Installed on an outdoor AC unit.


Above Schrader caps in box ready to ship. They come in a box of 10.

 Please click here if you are interested in a Box of 10 Model #JB NFT5-4 Quick Seal Schrader Valve Caps.

More on refrigeration leak detection:

Please click here if you are interested in the EasySeal Air Conditioner Leak repair kit.

I have other leak detection tools such as an alarm type electronic leak detector, $215.00 and a UV black light leak detection system $550.00. I think that finding refrigerant leaks is the hardest job any HVAC technician has to do. With the new EPA rules and regulations it is a must to find the leak and stop it, or I can face a huge fine. First, you visually look for refrigeration oil spots. This is a sure sign of a bad leak. If I can not visually see the leak I use my electronic leak detector, and if that doesn’t work I inject a bottle of florescent leak detection solution into the system let it circulate and try to search for the leak with a black light. The leak with show up bright yellow when the UV light hits it. The UV black light leak detection system needs to be done in low light conditions. Sometimes I ask the customer to come back after dark to find the leak or I crawl under a tarp to block the sun light out. This is really fun when it is 90 plus degrees out! Wow! You talk about hot! It is really cool and rewarding when you see that bright yellow leak shining back at you! You can show the customer exactly where the leak is too, but sometimes you have hidden areas that even the light can not detect. About 90% of the time it is the indoor evaporator coil leaking. It must be poor coil construction, added to the expansion and contraction of the metal during the heating and cooling seasons that cause these coils to leak. I replace on the average about 20 evaporator coils a summer! Some of these coil are only two to three years old. I can’t believe it! It is just poor construction. I would like to recommend that you get a warranty of at least 5 years on your air conditioning system that would include the indoor evaporator coil. Many times the coils are only warranted for one year. Thanks for reading my frustrations with finding refrigerant leaks. I hope that you do not end up with one of those leaking, out of warranty evaporator coils that I see every summer! God bless you and your family.

Problem 9: Why does my air conditioner’s condenser fan burn up so often?

Answer:  There are several things that can cause a fan motor to go out prematurely. I will list some of the causes below:

1. Installing a universal fan motor that is not matched correctly with the right RPM or horsepower to power the fan blade. Motors not matched to the diameter and pitch of the fan blade. Motors should be matched (RPM, Horsepower, Amps) with the fan blades or the motor will be over-loaded and the motor will fail soon.
2. Having a fan blade that is off-balance and causes vibration to the motor and unit. A new balanced blade would be best.
3. Installing a fan motor and capacitor where the capacitor does not match the specs on the label of the fan motor. The fan motor capacitor should match the specifications on the motor label.
4. Installing a fan motor where lots of moisture is present like from a leaking gutter or down spout. Water pours on to fan motor when it rains or when snow melts.
5. Not having the rain shield installed (when required) or leaving drain plugs open where water and moisture can get into the motor. Some motors have rain shields to prevent water from getting into the motor. Many universal motors do not have rain shields, but have drain plugs that can be opened or closed depending on how the motor is installed, horizontal, vertical, shaft up or shaft down.
6. Improper wiring. Where the motor is not wired according to the label on the motor.
7. Improper rotation of the fan blade. With the fan blade spinning in the wrong direction the motor will not load and it will burn up over time.
7. Grass, weeds, plants or children that stick into the fan blade path and stop or impede the fan motor when it is running.
If you would like to send your unit’s model number I will be happy to try and find out which OEM motor fits your unit. Our support email address is:

 What to Check for If Your Air Conditioning System is not Working:

1. Check the circuit breaker to make sure the breaker has not tripped. The breaker would probably be a double pole 30, 40 or 50 amp breaker. Even though the breaker looks like it is on I would still flip it all the way to off and back on again just to make sure. Sometimes one leg of a double pole breaker will hold in the other leg and make the breaker appear to look like it is, “ON” when it has actually been tripped.

2. Make sure your thermostat is turned down to a temperature that will allow the air conditioning system to come on. Sorry! I hope I did not insult your intelligence! I want to try to cover everything! I have been on several service calls when not having the thermostat turned down far enough was the only problem. If your thermostat has the little levers on it then it would not hurt to flip the little lever from “OFF” to “COOL”. On several service calls I have seen all that it takes is a flip of this little lever on the thermostat. Sometimes the contacts in the thermostat do not make the connection and flipping the levers will reestablish the connection. I would turn your fan to the “ON” position. Did the fan come on? If the fan did not come on check the switch on the side of your furnace to make sure it has not been turned to “OFF”. Make sure your filter access door and furnace door are secure. Many of the furnaces have a switch activated door for your safety. When the door is not completely on the furnace will not operation. This keeps the furnace from coming on when someone is servicing the blower or filter.

3. If your outdoor unit is running listen to determine if the fan is the only thing running or is the compressor running too?

4. Turn off your electrical power to the outdoor unit by pulling the disconnect switch or turn off the indoor circuit breaker. Take the screws off your air conditioner control access panel. Check with a multi-meter to make sure the power is actually off. Touch the top of the compressor. Is the compressor very hot? If the compressor is hot then the compressor could be out on thermal over-load. You need to wait and let the compressor cool down before you test your system again. Sometimes I use water from a hose and gently let it run over the compressor to cool it down quickly. Sometimes it can take 2 or 3 hours for a compressor to cool down. After it has cooled down reapply power. Did the compressor start? Did the fan start? If the fan did not start with the compressor then this is why the compressor over heated. Check your fan motor and fan run capacitor to make sure the fan blade is free and the capacitor is in good shape. You can check the fan bearings by spinning the blade by hand the blade should continue to spin 3 to 5 seconds after you spin it. If it doesn’t then you probably need a new fan motor. Another reason the compressor over heated could be that the system is low on refrigerant. Is the suction line (the line with the black insulation) cold like a cold coke can right out of the refrigerator after the unit runs for 10 to 15 minutes. If it is not cold, then you need to add some refrigerant. The refrigerant is what keeps the compressor running cool. If the system is low on refrigerant then you do not get the cool gas coming back to keep the compressor running cool. The compressor over heats, and this will eventually melt the windings down in the compressor and contaminant the whole refrigeration system! This is not good. Eventually the compressor will ground out and you will need a new compressor or new system. Please make sure that suction line is cold or you might be low on refrigerant charge. You will need to call a service technician to charge up your system if it is low. Now EPA require that you be licensed and certified to purchase and use refrigerants.

5. Inspect your wiring to make sure that you do not have any burnt connections. Repair the burnt connections if you have some.

6. Inspect the capacitor/capacitors to see if they are swollen looking. If they are swollen purchase a new capacitor from our capacitor page. Click here for Our Capacitors we sell Page.

7. Take the compressor terminal cover off and inspect the terminals on the compressor. Sometimes the compressor terminal cover can be a bear to take off. I use a screw driver to release the metal clip that holds the cover on. Sometimes the cover slides off. Sometimes the terminals unplug from the compressor. If any of the compressor terminals are burnt then you could probably use our Term-Lok compressor terminal repair kit to repair the terminals. Please see Term-Lok compressor terminal repair kit above on this page.

8. Inspect your contactor. Is your contactors points look burnt? You might need to purchase a contactor that we have listed above on this page.

9. When you plug in the disconnect and apply power to your outdoor unit does the fan start and the compressor try to start, but make a “UGGGG” sound. This means the compressor is locked up. The compressor is an electric motor, enclosed in a case, with a piston similar to what you would find in a car. When you hear that “UGGG” sound it is telling you that the piston is locked up. We need to try to unlock the piston. If we can not unlock the piston then you need a new compressor or air conditioning system. You might want to purchase a Super-Boost hard start capacitor. I have used this device to save many a compressor. The Super-Boost is also listed above on this page. If you purchase and hook-up the hard start capacitor and the compressor still will not start then I am afraid you will need a new compressor or system. I say, “System” instead of just outdoor unit because it is recommended that you change both the outdoor unit and the indoor evaporator coil when you install a new system. Manufacturer’s say that it will damage the outdoor unit if you do not change the evaporator coil too.

Best of luck! I hope this has helped you to trouble-shoot and repair your air conditioner! I hope you can get your air conditioner up and running again soon! I admire you for trying to repair your air conditioner yourself. Please be careful and make sure the power is turned off and you do not get cut on those sharp sheet-metal edges. Just take your time and think things out step-by-step.  If you have any questions please do not hesitate to email us and ask. Our email address is: God bless you and your family.

Sincerely, Steve Arnold, President,

Arnold’s Service Company, Inc.

115 thoughts on “Air Conditioning and Heat Pump Troubleshooting Simplified

  1. My ac has started behaving a bit odd recently. When cooling kicks in, inside the house the fan spins up but momentarily stop, then restarts. It does this 3 or 4 times and then runs constantly (until the thermostat shuts it off again). Any ideas what might be causing this?

    Thanks in advance for any tips.

    1. Hi Mark! You might have a thermostat relay going out or a blower motor that is going out. I would suggest taping the furnace blower door safety switch closed so you can do some testing with a volt meter set to “Volts AC”. Turn the thermostat down so that the AC comes on while testing with your volt meter between terminals. G (green) and C (common) on the control board. You should get a constant 24 to 28 volts AC between the G and C terminals. If you get the voltage dropping in and out then you probably either have a thermostat problem or a loose or shorted thermostat wire problem. If the voltage stays at a steady 24 to 28 volts Ac and the blower is going off and on then I would suggest turning off the power to the furnace and check to make sure the blower motor capacitor is in good shape. Some appliance parts places will test capacitors free. If the capacitor checks out OK then you might have a winding going out in your blower motor or if you have a high efficiency ECM blower motor then you might need a new blower motor module. I have an ECM motor on our Bryant 90I furnace. The blower motor started acting like what you describe and it was the motor module that was going out and I had to replace the module. This was not cheap. About $200! I hope you find an easy inexpensive solution to the problem. Hope you have a great day! Steve

  2. Hoping you can give me a “BS” check for a diagnosis by service-techs supervisor, over the phone, without tech reproducing the problem…

    I have a Carrier two-stage heat pump. Originally installed in 2005, replace compressor once under warranty. Also replaced compressor once out of warranty. Same Carrier-authorized company (large, local, with commercial and residential divisions) installed initially and has done the replacements. Recently started hearing a very loud grinding from compressor that resolves to normal compressor & fan noise after 2-3 seconds. I don’t know if it is only on long off cycles or if it occurs with short cycles. The A/C “seems” to be cooling adequately.

    The diagnosis by the service manager is “internal cam sticking between low-speed and high-speed cycles.” The tech didn’t test anything electrically or on the refrigerant. He said that it is unlikely that the compressor is getting liquid back, even though the evaporator is upstairs and has about a 30-foot run. His logic was that if the compressor was getting slugged with liquid that it would have condensation and would be growing algae or mildew. So, according to them, the compressor is failing and will have to be replaced. Someone is supposed to be contacting me with proposals to replace the current reciprocating compressor, or replace the entire external unit with one that has a scroll compressor.

    I would appreciate any thought you can offer. I hate to throw more money into a compressor, again. Thinking that an entire new exterior unit may be the best choice, since I just replaced (last September) the interior evaporator/coils due to leaks that “developed” over time. Of course, I’d hire a second opinion from another service facility if you suggest the explanation about the “cam” is BS. Thanks!

    David R

    1. Hi Mr. Reaves! Sorry to hear that you have had all those problems with your unit’s compressor! I do not think that a residential compressor has a cam, but maybe they are talking about the connecting rod. Maybe the connecting rod is loose and this would require a new compressor. Cams are mostly used in car motors to open and close the valves and not compressors. As far as I know most compressor valves open and close with compressor refrigerant pressure from the compressor’s piston. I would suggest that you replace the entire unit and replace the evaporator coil with a matched coil. The company should use the super heat method for charging your unit if you have a cap tube or piston metering device and the subcooling method to charge your system if you have a thermostatic expansion valve metering device. The pressures and temperatures should tell the technician if the unit is operating correctly and charged up correctly. I am sorry that I can not be much help. Steve

      1. Thanks. Maybe the connector rod is what they were calling a “cam.” Hopefully I can match a new condenser unit to the almost new Carrier evaporator coil that I spent over $2,000 on in the spring of 2016. It is the inside half of an Infinity system.

        I’ve been given quotes to replace the existing compressor with the same technology (which I won’t), to switch to a new, complete compressor/condenser unit single-stage (supposedly a scroll compressor), or a new complete compressor/condenser dual stage/possibly multi-stage.

        I’m going to find another authorized repair to ask for competing bids… the price for the two-stage compressor is VERY high. I’m reluctant to change the condenser unit to a single speed since that could kill the efficiency I was trying to get with the Infinity to begin with. I’m still waiting for the written quotes with equipment specifications, so I don’t really know what they are offering.

        Thanks again for the response.

  3. Hi,
    Hope you can help. I have a Goodman unit that is working fine and cooling the house. I have just noticed that the outside fan comes on randomly with the thermostat off in the house. The fan will run for about 4-8 minutes and then shut itself off. This goes on all day. I have checked the contactor and that is fine. The thermostat seems to be working fine and keeping temperature when it is on. I am at a loss. Thanks for your help.

    1. Hi Akin! I would check to see if the contactor is energized (closed) when the fan comes on. If the contactor is not energized (closed) when the fan comes on then you probably either have a short in the wires that go to the fan motor or the motor windings are shorting out. You might need a new motor. I would inspect the wires that run in a tube (pipe) to make sure the wires have not shorted together. I had a fan motor doing the same as you described, but it was running in slow motion (low rpms) and it was because two of the wires going to the motor had shorted out. I hope you can easily find and fix the problem. Steve

  4. Hi Mr. Arnold,

    I have a Trane xl80 gas furnace installed in an interior closet with a 50A51-405 Control board. As it got warmer here in Texas, I noticed the unit running almost constantly, often with the blower sounding like it was at low speed. Sometimes it will stop and then almost immediately start back up.

    Further investigation shows that this is the interior blower running, not the compressor. Control unit is blinking 5, indicating Flame Sensed with Gas Valve Closed. I have disconnected and later reconnected every furnace sensor with no apparent impact. I’ve cleaned the flame sensor. I’ve left it disconnected. Late evenings, it cuts off for longer behaving almost normally by morning. So there seems to be some thermal aspect to the problem. The closet is warmer than the house since there is air flow to the attic for the furnace. But it is not like an oven. Any guesses before I invest in your new 50A51-495 controller?

    We did have a series of storms a couple of months back. I would have already replaced the controller except for the odd “gets better at night” aspect. I’m no pro at this so figure I must have missed checking some probe or sensor or voltage the correct way.


    1. Hi Dean! I would suggest that you test the limit control with a volt meter to see if the limit is opening up and causing the furnace blower to run. If any of the rollout switches or if the limit is open then it will cause the blower to run because the furnace thinks it has over-heated and it thinks it needs to get rid of the heat inside the furnace. I would also check to make sure power is not coming from the green thermostat wire to make the blower run. If you have a shorted thermostat wire or a faulty thermostat this might make the blower run by energizing the green fan on wire when it is not supposed to. If all these check out OK then you probably need a control board. I would also make sure the blower motor capacitor is in good shape. I hope you can easily find and fix the problem. Steve

    2. I am a tech and have been doing this for 16 years and this is a first for me. I am working on a mobile home unit with down draft blower. owners called said inside unit freezing up and could not get blower to turn back on. First thing I did was clean it because it looked somewhat stopped up and not as bad a few I have been too. outside pressures are good. The mobile home was hot and had 70# on the suction and about 200# on the high side. Got it all cleaned up, turned on, stayed for about 2 hours trailer was 89 degrees, dropped to 84 before I left, blower amp draw was around 4.2 amps. Get a call at 6:30 in the morning ac froze up with light frost because tstat calling for cooling, but blower is not running. the place is only a mile from my shop so I run there put hand on back of blower, ice cold, not warm at all, put tstat to off position from cool, condensing unit shuts off. I test it out check all tstat lines for tightness under wire nuts at unit and screws at tstat. every thing looks good. Tstat wire from unit to tstat is attic run in the trailer so no chance of rat or rodent chewing under the trailer. Change out tstat and blower relay. Called again this morning at 6:30 same thing. She says it shuts on and off with the set temp of tstat. For ex: set to 72 runs to 72 shuts off gets above 72 comes back on. Thing is they are not noticing for me whether outside is shutting off or not after the long runs. I was thinking blower over loads bad, but not sure and do not want to just keep changing out parts. HELP

      1. Hi Jennifer! It sounds like the motor is shutting off for no reason. I would suggest that you test the blower motor capacitor to make sure it is in good shape. This is going to be hard to troubleshoot since you almost have to be there when the problem occurs. I would suggest setting the thermostat to “Fan ON” and see if the fan goes off, then if the fan does go off test with your volt meter to determine whether it is the fan motor not getting voltage, thermostat not supplying 24 volts through the green wire or motor over-heating. You could tell your customer to turn the fan to “Fan On” so you do not have to make an extra trip and see what happens. Another problem might be in the refrigerant charge. With the mobile home hot I would think that you would have a higher suction pressure more than 70 psi (not unless the evaporator is partially frozen) and depending on the outdoor temperature, I would think the head pressure would be more than 200 not unless they have a high efficiency unit. I hope you can easily find and fix the problem. Steve

      2. This unit is a high efficiency outside unit, but standard mobile home 2 speed blower inside. I think someone else put a newer condensing unit on the trailer and it is a heat pump but has been there for years and the current people in it have had it for 4 years and this just started 2 weeks ago. If the blower stays running through the night in the on position, what would be my diagnosis, it already has new capacitor, blower relay, and tstat on it. I have contacted my customers and they are going to try the Fan ON thing tonight since this unit works good all day and is only doing it at 4:30 to 6:30 in the morning. when they called me the first time, I ran over there and felt the blower but it was ice cold. Thank you for your earlier reply. Will see what happens in the morning. If the blower does shut off, what are some of the other things I could check. It is like something is locking the blower out and the condenser is still running, only other thing I could think of is defrost control board outside, but should not have anything to do with blower and figured it would just cause the outside to freeze up or not run. Any more recommendations would be greatly appreciated, like I said, I can usually figure these things out quickly not sure with this one though.

      3. Hi Jennifer! I do not see what the defrost board would have to do with the indoor blower shutting off. It would control the outdoor fan, but not the indoor blower. I would guess it would be a thermostat problem if the blower runs all night in the “Fan On” position and does not run all night in the “Auto” position. If you can check various controls like fan relay, green wire coming from thermostat with a volt meter when the fan is off then this should tell you where the problem is. Also check the voltage going to the fan to make sure it is getting 210 to 245 volts AC. This could be hard to do since the fan is working erratically. I hope you can find the problem soon. Steve

  5. I have a York air conditioner condenser with a brand new Goodman inside air handler with brand new inside evaporating a/c coils. Ever since the air handler was replaced, i have an intermittent problem with the condenser unit turning off when it reaches the temperature set on the thermostat, however the air handler continues to run until we realize the temperature in the house is going up (because the condenser unit does not come back on). I then manually turn the thermostat off and then on again and the condenser and the air handler come back on as if nothing happened. It will run fine for 2 to 3 days and then lo and behold I have to repeat the whole process. I had the hvac man check the air handler and he could not find any problem with it. Any thoughts will be most appreciated

    1. Hi Laura! Sorry to hear you are having problems with you air conditioning system. This sounds like a thermostat problem or a loose thermostat wire problem. The thermostat should send 24 volts through the “G” green thermostat wire and 24 volts through the “Y” thermostat wire when the thermostat is calling for cooling. The green wire controls the indoor air handler fan relay and the yellow “Y” controls the out door condensing unit contactor which turns the outdoor condensing unit ON. So with the air conditioner turned ON you should get 24 to 28 volts AC between G and C (com) and 24 volts between “Y” and C (com). If you are not getting 24 volts between these connections then you have a thermostat problem or a loose thermostat wire problem. This could be hard to determine since the problem has to be occurring when you do the testing. I hope you can easily find and fix the problem. Steve

  6. Hi Steve. I’ve been doing a lot of research this morning to determine whether we need a new capacitor or compressor. We have a Lennox 4HP 13/14 Split System Heat Pump. We just started using our air conditioning (bought house last year – fyi, system installed 2006) and though cold air blows out, it’s not very cold. (approx. 10 degrees less than inside temp). What are your thoughts?

    1. Hi Kini! Most of the time when an air conditioner is not cooling properly it is caused by being low on refrigerant charge. I would suggest using the feel test method on your air conditioner’s suction line to see if your heat pump is charged properly. With the air conditioner/heat pump running in cool mode, get under the black insulation of your air conditioner’s suction line. With the AC running this line should feel cold like a cold coke can right out of the refrigerator. If it is not cold then your unit is probably low on charge and you would need to call someone to find the leak and charge it up. Other causes for poor cooling would be dirty filter, dirty, stopped up evaporator coil, dirty outdoor condensing unit, dirty blower wheel, slow blower motor (might need a new blower motor capacitor). On a heat pump sometimes the reversing valve will not shift completely and sometimes a sequencer on the electric heaters will stay on running up the electric bill and giving very poor cooling. If your meter is spinning fast then more than likely you have a stuck heater sequencer. You might want to call a service tech to check this out, because most people do not have the guages and tools to troubleshoot air conditioners and heat pumps. I am sorry, but there are lots of things that can cause poor cooling. I hope you can easily find and fix the problem. Steve

  7. I have a frigidaire window unit that is digital, and the display seems fine. The dual run capacitor looks fine and the fan runs great, but I don’t think the compressor is coming on. Overload tests fine and compressor seems to as well when I use the ohms test, but when the unit is running, I only see about 66vac at all three of the terminals on the LG compressor. Any ideas? thx in advance, Doug.

    1. Hi! I am sorry, but I do not know much about window air conditioners. I would think that from each terminal to ground (neutral) would be 110 to 125 volts AC. Low voltage could be caused by too small of an extension cord or a loose wire connection somewhere. My only suggestion would be to make sure all connections are good and tight and not run the AC on an extension cord. You might have a set of contacts that are going out in one of the internal parts of the air conditioner that could be causing the low voltage. I would suggest having the capacitor checked to make sure it is in good shape. Some appliance parts shops will test capacitors free of charge. I hope you can easily find and fix the problem. Steve

  8. We have a Trane High Efficiency XB 1000 5 ton unit outside that is 16 years old. It seems to run OK (puts out cold in the summer), but it is very loud. It also draws about 28 amps when running without a load. Any thoughts on what might be causing it to run so loudly or pull so many amps?

    1. Hi Rob! A 5 ton unit is pretty big and some of the XE1000 units are loud because of the big compressor and not having a compressor cover to quieten the compressor down. I would suggest looking a the “RLA” on your unit’s spec label and see what the recommended Running Load Amps are. If 28 amps is above the recommended RLA then I would suggest that you look into things that would cause high amp readings like looking into cleaning the outdoor condensing coil. Make sure the condenser fan motor is running up to speed and the run capacitor for the fan motor is in good shape. Make sure the unit is charged up properly. An over-charge of refrigerant can cause high head pressure. If your unit has a thermostatic expansion valve make sure it is working properly and it you have a piston pin metering device make sure it is not clogged up. You should be able to analyze this by using gauges. An old compressor where the piston is getting tight can cause high amp readings too. If nothing works and you can not stand the noise then I would suggest looking into getting a compressor cover to isolate the noise or get a new unit. I know some of the new high efficiency units are super quiet. Here is what I found when I Googled this subject: I hope you can easily find and fix the problem. Steve

  9. Steve, I have a Heat Controller HP Series system with CMX control , Problem no fault lights, Fan runs followed the flow chart checked wiring,again no fault codes steady green operation leds, reset power came on as expected no faults, tstat wiring good no faults leads me to compressor overloads how do I find them to replace ?

    1. Hi Mr. Radeka! I am sorry, but I am not familiar with the Heat Controller system with “CMX” control. If this is a high tech system you will probably need special analyzing tools and equipment to find the problem. Most compressor overloads are located inside the compressor where you can not get to them. Most compressors have an internal thermal overload to protect them from over-heating and a high pressure relief valve over-load to keep the compressor from blowing up. There are refrigerant high and low pressure over-loads which do not allow the compressor to run if the pressures are too high or too low in the system. Sorry that I can not be of much help.

  10. My 4 ton Trane air conditioner stopped cooling although all motors are operating.
    Stuck the guages on without the system running and the low pressure was about 130 psi with 0 pressure on the high side.
    Does that sound like expansion valve failure?

    1. Hi! Yes, this sounds like either and expansion valve problem or another refrigerant flow valve that is closed and not allowing the refrigerant to flow through the system. This sounds like the low side is sucking down because of a blockage in the system. I hope you can get it fixed soon.

  11. I just purchased a New Trane Seer 16 -4 ton 4TWR6048H1 . They installed Thursday May 25, 2017. When the installers left it was making a bug zapper sound constantly, but they told me they could not find any mechanical issue. They said they would get Lead Tech out the next day to address the issue (they left at 7pm). I did have air but the Lead Tech did not show up Friday. Friday night at 7pm my house became unbearably warm. Upon investigating, I found my air exchange was working ( indicator lights showed no issues- good working condition) , but my outdoor unit was off. I did all the cursory checks to no avail, so I called for emergency service. Lead Tech came out, could not find problem. He stated the air handler should have triggered indicator light. He could not get the unit to start up. He stated he was going to have their Trane Specialist out ASAP to diagnosis the issue. He came today Monday. said it is the reversing valve. Stated he would have to remove and re-weld new one on…. I have requested a complete new unit since he did not address the air handler or the unit shut down. Does the reversal valve cause a bug zapping sound and am I right in asking for a completely new unit? I don’t want a Lemon from the start. Thank You Anne

    1. I would demand a new unit since they have to open the refrigerant system to replace the reversing valve. Anytime that a refrigeration system is opened you take the chance of moisture and dirt getting into the system which could spell trouble later on. You paid for a new system that should work properly from the start so you should get a new system that does not need a new reversing valve. When I was doing installs I had a brand new unit where the compressor would not start. The brand new compressor was locked up on start-up. The manufacturer would not give me a new unit, but only wanted to replace the compressor under warranty. I felt terrible that my customer did not have air and I ended up replacing the unit with a new one at my expense, then I took the unit back to our shop and replaced the compressor when I had time. I was able to sell the unit where I had replaced the compressor later in which I gave a special price because it had a replaced compressor. I think this is what the company that you had should do. Give you a new unit and then take the unit you have now with a bad reversing valve and replace the reversing valve back at their shop. They should be able to sell the unit without any problems at a later date. I hope you can get this straightened out. Steve

  12. I have a 1999 Trane XE 1200 heat pump and air handler. I came home to a warm house and heat pump and air handler wont run. I have power on both sides of Breaker. The outside unit will run if you push on electrical contact block in outside unit. Both compressor and fan run. Air handler will not run even in Fan only mode. Could the Transformer shut down everything. This unit does not have door switches or water level cutoff. Unit was working great up till now.

    1. This sounds like a low voltage problem which could be a transformer, thermostat, thermostat wire problem or a refrigerant safety control problem. You would need to start testing with a volt meter set to “Volts AC” starting at the air handler between the Red and Common wires to see if you have 24 volts AC between these wires. With the thermostat calling for cooling you should have 24 volts between the Y and C (com) connections if you do not then you have a thermostat problem or a broken thermostat wire. We have lots of troubleshooting advice and videos on the following pages: and If you unit is low on charge sometimes the low pressure switch will not allow the contactor to close. I hope you can easily find and fix the problem. Steve

  13. Hello,
    I recently purchased a Rudd RQPL-B048jk Heat pump package unit with 15kw heat strips. I have been having a hard time hooking up the thermostat to the unit. Inside the unit are 6 wires for a thermostat hook up, Blue, Red, Green, White, Yellow, and Brown (Brown was wrapped up inside). When I hook up the wires with Red(R), Green(G), Yellow(Y), Blue(C), White(W2) I get the Cold to kick on but also the heat strips turn on as well, and it occasionally switches to the Heat Pump and blows hot air. I have had to disconnect the White wire to keep the unit from switching the heat strips on while cooling. I have 2 thermostats one that came with my original Heat pump that has wiring for R,Y,G,C,W,O and another that is a ritetemp 6080. Can you help me with how to wire this unit in correctly?

    1. Hi Nick! Most of the time heat pumps are wired like the picture on the following page: You should have 6 wires and rule of thumb like in the picture should be wired R=24 volt power, W=Electric heat, Y=cool which is connected to the outdoor heat pump’s contactor, G=Indoor fan relay which turns the indoor fan off and ON, C=24 volt common wire and O=the reversing valve wire. The O energizes the reversing valve to shift the heat pump’s reversing valve from heat to cooling. I would suggest that you trace your thermostat wires to see where each of the wires go on your air handler and outdoor unit. If you are in the cool mode and the heat strips are coming on then of course this means that which ever wire that controls the heat strips is wired wrong. Most heat pumps energize the reversing valve in the cooling mode. I do not know if Rheem heat pumps do this or not. Maybe you have the reversing valve wire “O” and the “W” wire reversed. I would suggest tracing down each wire to see where it goes. I will be glad to try and answer any questions after you find out where the low voltage thermostat wires terminate (see what they are controlling). I hope you and easily find and fix the problem. Steve

      1. Thanks Steve but my Ruud dose not have a orange wire in it & its a heat pump its driving my crazy & you can guess. It puts out 47 out of the vent sometimes or 60 & then sometimes 70 & runs most of the time I just dont no what else to do. Thanks again

      2. Hi Nick! If the varying temperatures are not being caused by the electric heater coming on, then I have heard that many of the heat pumps have had trouble with the TXV (thermostatic expansion valves) becoming stopped up and causing the heat pumps not to heat and cool properly. You might want to check the pressures with guages and see if the pressures are normal and make sure the heat pump is charged up properly. I believe that on Rheem, Ruud the reversing valve is energized in the heating mode. You would need to determine which wire is used to energize the reversing valve and then set your thermostat so that it energizes the reversing valve in the heating mode. I found this on the following website page: I hope this helps solve the problem. Steve

  14. I’ve got a head-scratcher of a problem with American Standard air conditioner. The compressor fan runs continuously, even when the compressor is not running.
    It has a single pole contactor with a bus bar on one leg of the 240V power. So the single pole contactor is supposed to power on both the compressor and the fan motor.
    I checked the contactor for low resistance from terminal to ground as well as the dual capacitor for low resistance between terminal and case. I used 200k setting on DMM.
    Fan connections also normal with high resistance to case.
    Have you heard of such a problem?

    1. Hi Dave! I had this problem before with some of my customers. I found that some of the fan wires were ground out (touching each other where the insullation had worn) inside the conduit that runs to the fan motor. This can also be cause by a motor winding that has grounded out. You might need a new motor to correct this problem. If you want me to look up the motor part number please send me your unit’s model number. I hope you can easily find and fix the problem. Steve

  15. I have a goodman heat pump sytem the heat works great but if i turn to a/c everything seems to come on but insulated line coming in is hot right away and blows warm air. Tried replacing defrost board but same issue.
    Thanks for the help

    1. This sounds like you might have a stuck reversing valve. This could be caused by the “O” connection on the thermostat not sending 24 volts to energize the reversing valve solenoid. Could be caused by a burn out reversing valve solenoid or a stuck reversing valve. A low refrigerant charge can also cause a reversing valve not to shift. I would suggest making sure the reversing valve coil is getting 24 to 28 volts AC from the thermostat. I hope you can easily find and fix the problem. Steve

  16. Yes I have a Goodman heat pump in a mobile home. When I cut the a/c on the evaporator immediately starts to freeze and switch it off it unthaws. I can cut the heat on and the heat works fine. It seems like the only time I have trouble is when it is switched from heat to a/c.

    Thanks, Joe

    1. Hi Joe! Sounds like maybe the blower motor is not working when your air conditioner out door unit is on. This could be a thermostat problem or a blower motor relay problem. Some units have control boards that control the fan and some have relays or sequencers that control the blower fan. Freeze up conditions can also be caused by a system that is low on refrigerant (Freon). We discuss this problem on the following page: I hope you can easily find and fix the problem. Steve

  17. Hello. I have a Trane xi14 compressor that is locked up. Draws full amps until fuses pop and or breaker flips. It makes that low uurrrrrr groaning before blowing fuses. I have three questions. Could a loose yellow wire in the homes thermostat have caused this compressor lock up? Second question is. How do you feel about changing out just the compressor if all other components look to be in good shape in the system? One last question. How about the rap rap with a hammer to the side of this compressor to get it to start ?

    1. Hi Leo! This sounds like the compressor is locked up. Before thinking about a new unit I would suggest turning off the power to the unit and checking all wire connections to make sure they are all tight and in good condition (not burnt). Yes, a loose yellow wire on the thermostat could cause a poor connection with the contactor, cause contactor chatter and burn the contactor up. I would suggest checking the contactor contacts to make sure they are in good shape. I would suggest making sure that your unit’s run capacitor is in good shape and up to specs. I would not rap the compressor with a hammer, but would invest in an SPP6 hard start booster which we sell on the following page: Depending on the age of the unit and the condition of the refrigerant oil in the system. If it is over 10 years old I would suggest replacing the whole system. If your contractor does an acid test and finds the refrigerant to be acidic then I would suggest replacing the whole system. I hope you can easily find and fix this problem soon! Steve

  18. Thank you so much for such an informative site. I have a heat pump unit. The fan would not shut off even though the system outside would cycle on and off – both heat and cool. We intended to replace the thermostat, but after removing it, realized we had ordered the wrong one. After putting the old thermostat back on, the outside unit will not come on. We have replaced the fuse in the attic part of the unit (twice), but still get nothing. We have replaced the control board, also. We can hear the capacitor hum, but it doesn’t sound like power is even getting to anything else. The fan turns freely and was replaced last year. What is my next step? Thank you in advance for your help.

    1. Hi! I am sorry to hear that you are having problems with your heat pump. This sounds like either you have the thermostat wired wrong or the thermostat wires might be shorted out. Most of the time in troubleshooting it will require a volt meter. I would suggest that if you do not have a volt meter, then turn off the power to the unit take the thermostat wires loose and join the red (power wire) and yellow wires along with the green wire. The red is the hot power wire and the yellow should energize the contactor on the outdoor unit to make it come on. The red and green connection should make the indoor blower fan come on. After you join these three wires together turn the power back on and see it the outdoor unit comes on and the fan (blower) comes on. If it doesn’t then you probably have a blown fuse or the thermostat wires are shorted out. With joining the 3 wires together you will probably be in the heating mode. On most heat pumps the “O” connection energizes the reversing valve so cooling comes on. If you do not want to join the wires together for this test, then I would suggest getting a volt meter and test between R and C to make sure you are getting 24 to 28 volts AC at the thermostat. If you aren’t getting 24 volts between R and C then you probably have a blown fuse of a bad transformer. We have lots of troubleshooting advice on the following pages: and I hope you can find and fix the problem soon.

  19. Is you’re address not working ! Can sup cap be used to start a window unit sylvania 15 k it starts runs 10 seconds cuts out fan still running. The cap can’t fit in window unit looks like can I jus use to start the put back in old ?

    1. Hi Tom! Sorry for the delay in answering your question. We have had a busy day. Yes, you could try the Supco SPP6 to see if it helps in starting the compressor in your window unit. Yes, you could install it to see if it will start the compressor and remove it if it does not fit. I would suggest making sure that your unit’s run capacitor is in good shape before trying the SPP6. If your run capacitor is good and the SPP6 does not start your compressor then more than likely you are going to need a new compressor. I hope you do not need a new compressor or new unit! I hope you can get your unit fixed soon. Steve

  20. The inside blower motor fuse burns up as soon as the power is added. I can have the thermostat in the off position but the moment I turn on the heat or ac the fuse burns out. Is it the thermostat or could it be the capacitor.

    1. Hi Pete! Most of the time fuses are on the control board. If the low voltage control board fuse is burning up then you probably have a short to ground in some of the thermostat wires. We discuss this on the following page: If this is a high voltage fuse (110 volt) that is burning up then more than likely your blower motor or AC compressor has a short to ground and one of them might need to be replaced. I hope you can easily find and fix the problem. Steve

  21. How do I know whether I have a time delay fuse or a fast acting fuse on my thermostat board? 5A 250 is all that is printed on the fuse that is on the board now.

    1. I have never seen a time delayed fuse on a furnace control board. Most of the fuses can be bought at a hardware or auto parts store. You would not want a time delayed fuse on a control board because it would allow time to harm other electrical parts and components. Since I have never seen a time delayed fuse on a furnace I do not know how to identify one. We sell some 5 amp fuses on the following page: We also sell a handy testing tool if you are burning up lots of fuses on the following page: I hope you have a great day. Steve

  22. I’ve replaced the 24 volt transformer twice in the last 2 months. I noticed this last time that both the inside and outside fans make an intermittent chattering noise. However, if I just set the thermostat to “fan” it works fine. Could it be a bad relay or a bad connection somewhere?

    1. Hi David! If the outdoor unit’s contactor is chattering then this is a sure sign that it isn’t getting enough voltage. I would suggest checking the low voltage coil on the contactor to make sure you are getting a minimum of 24 volts AC when the unit is on. If the transformer is having to be replaced you might have a slight short in the thermostat wires. I would suggest visually inspecting the wires to make sure they look OK and are not pinched anywhere. A higher VA transformer might help too. Most transformers are 40 VA. A heat pump with emergency heat controls, contactor and reversing valve can be hard on a transformer. A 40 VA transformer should handle all these heat pump controls. If your thermostat has batteries I would suggest you make sure they are in good shape. Since your unit runs fin in emergency heat you could have a short in the wires that control the outdoor unit. I hope you can easily find and fix the problem. Steve

  23. will it damaged the heat pump if fan does not come on?need to run until they can come out to fix it.

    1. Hi Dennis! Yes, it can damage the heat pump if the fan does not come on. If it is the outdoor fan that is not coming on then I would suggest that you go to emergency heat. Emergency heat on the thermostat should shut the outdoor unit off and heat your home by using your auxilary heat only. If the indoor fan will not come on then you had better wait until you can get the indoor unit repaired. I hope you can get it fixed soon. Steve

  24. Trane Heat Pump with Zonex control board DTHP4A. Cooling works fine. Upon heat call or emergency heat call, compressor never energizes.

    1. Hi Larry! If you have the thermostat set to emergency heat the heat pump outdoor unit should not come on, but your auxilary heat and air handler should work. If your outdoor unit will not come on off of emergency heat, then I would start by looking at the thermostat. On most heat pumps the “Y” connection, yellow wire on the thermostat goes directly to the contactor to energize the contactor. If you do not have 24 to 28 volts at the contactor then you might have a thermostat problem or a broken or loose thermostat wire. The control board in most heat pumps does not have anything to do with the contactor coming on to start the outdoor unit. Best of luck in finding and fixing the problem. Steve

  25. We have a 14 year old split system Trane. It’s winter and the unit kept blowing cool air. I set the thermostat for emergency heat and it worked fine. The serviceman said it was a faulty valve in the outside unit (maybe he said expansion valve). The compressor was hot. Cost would be 900 to 1200 or replace the system. I can’t afford either right now, but can keep using the em. heat setting. Also, we bought a space heater and that works good.

    1. Hi Paul! I am very sorry to hear that you might need a new unit during the Holiday Season! Your service man could be either referring to the expansion valve or the reversing valve. Both are real expensive to repair and replace. Since the compressor is getting hot more than likely it is the expansion valve. Considering the age of your heat pump it would probably be best to get a new heat pump system. They say since you have a heat pump that is 14 years old it is like having an air conditioner that is 28 years old because the heat pump runs both winter and summer. You might want to get another opinion to be safe. Sorry for your trouble. I wish I could help you out! Steve

  26. Where do you put a ground wire on a window air conditioner with heat?

    1. Hi! Your window unit should be automatically grounded through the plug on your window unit if the plug that your window unit plugs into is grounded at the circuit breaker box. This ground is sometimes referred to as a safety ground and is connected to the metal body of the unit so if there is a short to the ground of the body of the unit it will blow the circuit breaker and not shock you. If you want to ground something like a new window unit motor you would attach the green wire to the body of the window unit. I hope that I have answered your question. Hope you have a great day! Steve

  27. Thanks for such a great site. I have a Tempstar heat pump package unit. The compressor and fan work when the thermostat is set to cold. It cools the house great. When we recently switched it over to heat, the fan and compressor does not run, however the blower does. No warm air. Switching it back to cold, and the air works fine. Any idea where to start looking for the problem? Thanks much.

    1. Hi Mark! Thanks so much for your kind words! I would start by checking the thermostat to make sure it is working correctly. The thermostat on a heat pump when calling for heat in the winter time should energize the Y for the outdoor unit contactor, and G for the indoor blower motor. Most heat pumps do not energize the reversing valve in the heating mode so the O connection should not be energized. If like you say the outdoor unit is not coming on then I would think that the Y wire is not being energized so I would check the thermostat. I hope you can easily find and fix the problem. Steve

  28. I have a 16 by 80 trailer with the furnace in the hall and an outdoor unit outside. ive had troubles similar to what some of the guys have explained on here already with blowing the low voltage transformers and thanks to your website figured out that problem was from naked thermostat wires here and there. well I ran a new thermostat wire and installed a new transformer and my main goal was to get my heat going for this winter. and wala the furnace unit in hall heated up and fan below it kicked on and im blowing heat out my vents. my only question is the outdoor unit is not running and its been 2 years since ive used heat with this unit so my question is is the outdoor unit supposed to be running and kicking off and on with heat or is that just for cool

    1. Hi James! Thanks so much for the question. Congratulations on getting the furnace going! If you have a heat pump unit, then the unit on the outside will run in the heating mode during the winter time. If you do not have a heat pump and have gas or electric heat then the outdoor unit will not run. The outdoor unit will only run in the air conditioning mode if you do not have a heat pump and have electric or gas heat. I hope you have a great day! Steve

  29. Yesterday I was mowing my yard and the brown line connecting to the outside unit got pulled when I was using my weed eater. Well the unit stopped working of course but my fan on the inside was still working. Well I called a company to come fix it in which he did. The problem came when turning the unit back on. It did nit come on. He did not flip the breaker when he was messing with it. So he goes to my motherboard and did some tests and said it was blown. Well I was looking up OEM motherboards online and saw they were pricey. But I wanted a second opinion so I called a coworker who is hvac certified and he ran some tests and showed me that the transformer was not supplying the 24 volts to the motherboard but the power was being supplied to the transformer. The fuse was not blown on the motherboard either. I was just wanting some to let me know if the transformer is blown due to the guy not cutting the power when he fixed it or what. And what potential problems could come next seeing the transformer was damaged.

    1. Hi Antron! I have seen and had to repair, many times thermostat wires that have been cut by weed-eaters or sheers over the years. It sounds like the damage was done, either when the wires were cut with the weed-eater or when the service tech did the repair without turning the power off. It sounds like the transformer secondary was fried. You should be getting 24 to 28 volts AC between the R and C (com) terminals on your control board. I would suggest that you try replacing the transformer with a new one first before replacing the control board. Hope that the new transformer will fix the problem. Best of luck. Steve

  30. Great site you have. I have a 2-ton York outside air conditioner. Everything works fine, but I noticed that the top of the fan is slightly warm and hums a bite. Seems like it is getting some type of power going into the fan motor. The only way the humming goes away is when I pull the breaker. As mentioned, everything works fine, but I am concern that I’m using unnessary power somehow.

    1. Hi Mr. Cervantez! Thanks so much for your kind words and the question. If you fan is humming with the contactor open and the thermostat not calling for cooling then you might have a shorted winding or slight short in one of the wires that are going to the fan motor. Please disconnect the power to the unit before inspecting or troubleshooting your unit. I would suggest that you make sure it is the fan motor that is humming and not a reversing valve solenoid or a transformer on your outside unit. We discuss this hum noise with the unit not running on the following page: I hope you can easily find and fix the problem. Steve

  31. I have a 5 ton goodman comfort tech ac that keeps eating capacitors. They’re not budging, and I haven’t tested them, but when swapped in a new one, it runs fine for a day or 2, sometimes a week. Had a tech tell me starting a hard to start compressor would do this, low voltage or high pressure due to txv, and said it wouldn’t hurt to install hard start kit (start relay). The unit used to have 6 flashes, start problems, but now sends 8 flashes, high line voltage, after the start capacitor and relay installation. The unit runs fine and cools/dehumidifies the house perfectly when running. Going to test the voltage at contactor when I get home today, after reading your site, but was wondering if you have any suggestions for a part that would be causing this?

    1. Hi ToastyInTexas! I would suggest that you make sure that all wire connections are good and tight especially the contactor connections, disconnect connections, compressor wire connections and capacitor connections. A loose connection can cause high amperage draw. I would also check to make sure that the contactor is getting a minimum of 24 volts AC. A contactor that chatters can cause capacitors to blow. If you do not have a hard start capacitor booster installed I would suggest that you get one installed. We sell the SPP6 on the following page: Yes, I would suggest that you check the voltage coming into and going out of the contactor when the unit starts. Best of luck in finding and fixing the problem. Steve

  32. Good article!
    Have a strange one though. I have a Trane 5 ton 14 seer split system outdoor unit that popped a breaker. I disconnected the disconnect then closed the breaker and reconnected the power. The compressor struggled to start, then sounded like it was really loading up then would shut down (compressor only). Tested the capacitors and they were fine. Changed the relay as well to no avail. Finally put hard start kit and it starts and runs but goes in and out of this heavy load sound in the compressor as well as it “clicking” or knocking as it does so but continues to run. Tested the compressor and got no opens or shorts and ohms were .8, 1.7 and 2.0. Seems compressor electrics are worn but nothing a hard start kit shouldn’t handle. Pressures are fine and until this incident it seemed to be working fine. This is making me nuts! Only thing I can come up with is an internal mechanical problem with the compressor.
    Your thoughts??

    1. Hi Brett
      If the pressures are fine like you say then I would say that you have a mechanical problem inside the compressor perhaps a valve or connecting rod going out. Many of the high efficiency compressors are scroll compressors and I know they do make quiet a bit of noise when they start and stop, but not much when running. I would suggest that you watch the pressures in your system while the unit is running in comparison of when the sound gets louder. Does the pressure on the high side go up and the low side go down? If it does then it sounds like you could have a restriction in the refrigeration system. I hear that many of the evaporator TXV valves (thermostatic expansion valves) are having problems getting stuck or opening and closing wrong because of a problem with the compressor oil and the internal TXV valve working parts. Many of the manufactures have had to recall the TXV valves. I would also suggest that you use and amprobe meter and see how many amps the compressor is running. If it is at or above FLA (full load amps) then you will probably need a new compressor before long. I hope you can easily find and fix the problem. Steve

  33. Hi Steve,

    Great write-up! But I couldn’t find an answer for my issue… I have a 5-ton Goodman heat pump. After bumping down the temperature from the saved setting, I noticed it starting to get warm inside and the air handler was still running. I check the outside unit and the fan was not turning, but the compressor was humming (seemed to be on anyways). I shut everything off and the breaker in the garage for a few minutes and everything kicked back on and started cooling with the saved temp setting.

    I again bumped the temp down on the thermostat and it again got warm. Nothing was running outside. I had to turn everything off again, circuit breaker and even had to pull the outside unit’s breaker out this time to get it running again.

    What’s goin’ on? I’ve bumped the temp down before with no issues. Thank you!

    1. Hi Aaron!
      This sounds like you might have a loose high voltage line connection or a contactor that is going out. I would suggest that you turn the electrical power off to the unit and do a through inspection of the wire connections, capacitor and contactor. If anything looks loose burnt or if the capacitor is bulging then you have found the problem. This could even be a loose connection in the breaker box, disconnect box or a breaker that is going out. Best of luck in finding and fixing the problem. We have a troubleshooting flow chart that I hope will help on the following page: Steve

  34. I have a problem with my heat pump that I couldn’t find listed here. When I turn on the AC, the air blows cold for a while, usually for an hour or two, and then it starts blowing warm air. If I turn it off and let it sit for a couple of hours, then it will start blowing cold air again. I thought maybe it was running low on refrigerant, but tonight I noticed something that I hadn’t noticed before. My wife had it running when I got home from work, and because it was so warm in the house, I checked the vent, and it was blowing warm air. I went upstairs to change my clothes, and I could hear the unit running outside. But as I was getting ready to go back downstairs and turn the unit off for a couple of hours, I heard what sounded like the compressor turn on. I went back downstairs a minute or two later to check, and sure enough it was blowing nice cold air. So in our case, the compressor still works, but it seems like it’s not kicking on and staying on like it’s supposed to. Any thoughts on what might be causing that?

    1. Hi Mike! This sounds like the compressor could be over-heating and going off on thermal over-load. The compressor has a thermostatic switch inside it that protects the compressor from over-heating. If the compressor gets too hot this thermostatic switch will open until the compressor cools down enough then the thermostatic switch will close to allow the compressor to run again until it over-heats. The next time the compressor shuts off and you are not getting any cool air coming out of the registers I would recommend that you shut the power off to the unit and feel the top of the compressor to see if it is hot. If the compressor is hot then it could be caused by a number of problems: (1) yes, the system could be low on charge, (2) the condenser coil could be dirty, (3) you could have a weak capacitor that is not allowing the condenser fan to run at full speed. We have a good troubleshooting flow chart on the following page: Best of luck in find and fixing the problem. Steve

  35. Hi, I have a roof top unit that the compressor is really hot, and is not cooling very good, the compressor stopped running after adding freon, it had a low pressure 30-40 and high head 350-360, any thoughts.

    1. Hi Regan! This sounds like the metering device either TXV (thermostatic expansion valve) or piston pin could be partially stopped up because your head pressure is too high and your low pressure is too low. This sounds like not enough refrigerant is getting into the evaporator coil. You will probably need a tech to check this out because it involves some special tools. I hope you can get this fixed easily and inexpensively. Steve

  36. Hey. my ac unit comes on and the outside unit fan blows. after a minute the compressor kicks on for about 3 seconds and then turns back off. it isnt humming or making any crazy noises. any idea?

    1. Hi Mr. Morrison! Thanks so much for the great question! I would suggest that you look and see if the contactor is staying closed or not. If the contactor is opening up after the 3 seconds then you could have a thermostat problem or a low pressure switch which is cutting the power off to the contactor. We discuss this problem on the following page: This problem could also be caused by a locked compressor that is trying to start then going off on internal over-load after 3 seconds. About the only way to see this is happening is with an amprobe meter that shows the amp draw of the compressor when it tries to start. Most compressors with draw 40 to 50 amps for a split second then go back to RLA. (running load amps) which is usually about 15 to 20 amps. If the compressor amperage draw is way up over 50 amps for 3 seconds or more, then it will cut the compressor off to protect the circuit by the compressor’s internal over-load. I would suggest that you make sure your compressor’s run capacitor is in good shape and not weak. A weak capacitor will cause a compressor not start properly. I hope you can easily find and fix the problem. Steve

  37. Good day
    My unit come on but do not blow hard just a little bit is blowing out of the vents what do I do

    1. Hi Sashjaa! Most of the time when you aren’t getting much air flow out of your air conditioner it is caused by the evaporator coil being frozen up with ice. We discuss this problem on the following page: I would also suggest making sure that your blower motor capacitor is in good shape and not weak. A weak capacitor will cause a blower motor to run slow. Best of luck in finding and fixing the problem. Steve

  38. Hi,

    I currently have problem with our AC. It keeps tripping off the breaker. The outdoor unit fan and the compressor (and the indoor unit) will run in few minutes, somethings it takes 2-cycles (the outdoor and indoor turns off, then it turns on again) but after a while, the outdoor until stops and it’s the indoor unit that keeps running and not longer cooling. When I checked the breaker, it tripped off. So I tried, turning on the breaker, and the outdoor runs again but again, it stop in few minutes of operation after it turns off and starts. and the breaker tripped off again.

    1. Hi! More than likely you have a loose wire or a breaker that is going bad. I would suggest having an electrician check the breaker to make sure it is in good shape and check all wire connections to make sure they are good and tight. A breaker that arcs on the inside or a loose wire that arcs causes high amperage draw and will trip the breaker. Sometimes if you listen closely in a quiet home you can hear the breaker arcing. An arcing breaker that is going bad will feel warm on the outside. Another cause for breakers on air conditioners blowing would be a compressor that is tight and is drawing too many amps. About the only way that I know of to test this is with a special meter called an amprobe. The amprobe can measure the amount of amps the compressor is running by clamping it around one of the compressor wires. I would have this checked out by an HVAC tech. The HVAC tech might be able to fix it if you have an electrical problem as well. Steve

  39. Hello, I have a 5ton trane model XE1000 TWR060C100A3. Recently the cap and contactor were burnt out and replaced and everything seems to be running smoothly until thermostat reaches set temp. When this happens outdoor unit fan stops running but sounds like compressor keeps running for a few minutes. I had a repair man check coolant pressures and he said that they look normal. But my questions is, should the compressor continue running without fan after set temp is reached? Thanks in advance

    1. Hi Mr. Reyes! No sir, the compressor should not run after the out door fan has stopped running. This is very hard on the compressor to run without the condenser fan and this creates high head pressure in the unit which over time can damage the unit. I see that your unit is a heat pump and has a defrost control. If the defrost control is not working properly then this could be your problem. The defrost control would cause the fan to stop and the compressor would continue to run only in the winter time when the heat pump needs defrosting. You might need a new defrost control or defrost sensors. Our parts program shows that your unit uses a CNT05001 defrost control with sensors SEN00347 and sensor SEN00182. I would have your technician out to see why the unit is running without the condenser fan. This could be the defrost control or another problem and he should be able to test and find out where the problem is coming from when the problem occurs. Hope you get this fixed soon! Steve

  40. What causes a transformer in the air handeler to keep burning out on a Heil split unit m# NTC5100BH?

    1. Hi Edwin! Thank you so very much for asking this question. We go over this problem on the following page: I hope this helps you find the problem. Steve

  41. Hi Arnold. I have, or had, a 4 ton Goodman AC unit which was installed in 2003. The AC unit compressor and fan suddenly stopped working. A technician from the power company came out to repair it. He first tested the fuses while they were still installed in the power drop and said they were still good. The capacitor was swollen so it was replaced but the unit still would not turn on. The technician then replaced a few more components but nothing seemed to work. The technician checked the new capacitor an stated he was getting 120 volts from both sides. He finally said it must be an internal thermal protection switch tripped and unfortunately that switch was not resettable so the unit would need to be replaced. When the unit was replaced, by a subcontractor for the power company, it behaved the same way my old unit did by not powering up. The subcontractor pulled the fuses out of the power drop and tested them. One fuse was found to be blown. He replaced both fuses and the unit came on.

    The technician who said my unit needed replaced denied he did anything wrong and his employer agreed with him because my old unit was crushed and recycled by the subcontractor before it could be inspected by another technician.

    My question is, after reading your posts, is it normal for the capacitor to read only 120 volts from each side or should it have been 240 volts?

    1. Hi Mr. Cline! So sorry to hear that you had this problem! Sounds like the technician from the power company did not know what he was doing. The only way to test a capacitor that I know of is with a capacitor tester. You can not use a voltage tester to test a capacitor. The meter or capacitor tester must be able to read “Uf” microfarads. We sell a good capacitor tester on the following page: Sorry to hear that they probably replaced your unit when you might not have needed one! Steve

  42. I have a american standard heat pump the outdoor fan want run and the comp want run replace the capacitor noting happen i have 24 volt at the coil the contactor pull in i have 230v going to comp nothing happen it have a circuit board on i think it is board.

    1. Hi William! If your contactor is energized (closed) and you are getting 23o volts to both the compressor and fan motor, and the neither the fan motor or compressor will run then I would think you have a bad fan motor and compressor. I have never seen both go out the same time. Please make sure everything is wired up correctly. Most of the time a control board is not the fault when both the compressor and fan do not work. Please send me your unit’s model number if you want me to look up parts. I hope you can find the problem easily. Steve

  43. Hi Steve, thank you for your wonderful website. I have a York 3 ton air conditioner that runs for days, weeks, months and then all of a sudden the compressor stops working. When I go outside the fan on the condenser is running and the blower is running and obviously it’s blowing hot air in the house. It’s actually starting to do this more often, now. To fix the problem I turn the thermostat off. If I turn the thermostat on too soon the cool down light on the thermostat blinks as if the compressor is turned off and cycle on too fast. I wait a little longer and turn the thermostat back on and the compressor kicks in. They are conditioner will run fine now for days or weeks. I’ve changed out the Dual capacitor. It was starting to go bad . That has not helped the problem. This air conditioner has a start capacitor and relay to boost voltage to the compressor. I’m going to change the start capacitor and relay to the compressor. I’m hoping that the relay or capacitor is bad. The only other thing that I can think of is a bad compressor. I’m hoping not. Do you have any suggestions.

    1. Hi Curt! Thanks for asking this question. Since the compressor runs for weeks and days after you reset the thermostat, then this could not be a compressor problem other than the compressor maybe overheating and going off on thermal over-load. The next time this problem happens I would suggest that you turn the power off to your unit and see it the compressor is hot. If it is real hot on top then you might be low on refrigerant charge and the low refrigerant is not keeping the compressor cool enough causing it to go off on thermal over-load. I do not understand why that resetting the thermostat fixes the problem other than maybe a relay on the thermostat or control board on your outdoor unit is becoming worn where it works sometimes and sometimes it does not work. It seems like if the thermostat was the problem nothing on the outdoor unit would work and you say that the fan is working and the compressor is not working when you have the problem. Please use the AC troubleshooting flow chart to find the problem the next time the problem occurs. We have this chart on the following page: We have lots of troubleshooting questions with answers and videos on the following page: Sorry, but this is one of those problems where you almost have to be there when the problem occurs to troubleshoot and find out where the problem is coming from. Steve

  44. My ac unit will run perfectly fine for weeks at a time and then suddenly the outside in it will shut down but the handler will continue to run. The breaker is NOT being tripped but if I turn breaker off then on unit will start up again and then run fine for days or weeks before it suddenly shuts down again. Any suggestions on problem would be appreciated iated.

    1. Hi Terri! This sounds like it might be a circuit breaker problem or a loose high voltage wire problem. You probably need to call an electrician to do this. You might want to check all wire connections going to the breaker and make sure they are all tight. Many times a breaker will look like it has not tripped, but actually it is tripped. This problem could be caused by a weak breaker where the contacts inside the breaker are arcing. I would suggest touching the outside of the breaker after your air conditioner has run for several hours and see if the breaker is warm. If it is warm then you need a new breaker. Please be careful when working with live electricity. You might want to get an HVAC tech or electrician to check this out. I hope you have a good night! Steve

  45. I have a York 3 ton split unit. Since I have purchased the unit back in 2010 I have had issues with it. The terrible contractor I used was of no help. I am trying to find out if my compressor needs to be replaced. This is the issue. I live in Arizona and when it gets hot the fan will turn on but the compressor does not. At least not for the first 3-5 minutes and then it kick starts and work great. But for the most part the compressor does not turn on when the fan does. When the weather is a little cooler (<95 degrees) I never have that issue with the compressor. Recently I repair company came out and said that the compressor would need to be replaced. My thought on it is that when the compressor works it is great, when its a little cooler it is great. Could there be something else causing this delay of the compressor to turn on. The other possibility I keep reading about is the capacitor going bad. What if the capacitor is fine and not casuing the issue should I replace it just in case? Also, in the past the repair company installed the hard start kit which did not seem to fix the problem. Please let me know if you need more information about the problem and/or the unit. Any suggestions would be greatly appreciated. Thank you!

    1. Hi Denis! I really do not know exactly why the compressor is delaying on start when it is hot. It must have something to do with the pressure in the system. The pressure in the system as you probably know is much higher when the temperature is high. The key is that the compressor is running fine when the temperature is lower. So I would not think you would need a new compressor. All that I can think of would be a high pressure sensor not allowing the compressor to come on or an internal thermal over-load not allowing the compressor to start until it cools down. This could be caused by an over-charge of refrigerant not allowing the compressor to start until the refrigerant is cooled down by the fan. Too much pressure until the refrigerant is cooled by the fan. You might want to turn the power off to the unit and see if the compressor is hot when this happens. I know that it is very important that you outdoor condensing coil be clean as a whistle when the temperature is 95 or above. Please make sure you have a clean coil. You might want to try and call the compressor manufacturer and see if they have any suggestions. I hope one of our followers will comment and help you out. Thanks so much for asking this great question! Steve

  46. Why would the blower relay keep burning up runs for awhile 4or more hrs

    1. Hi Craig! Most of the time blower relays burn up due to loose wire connections, improper wire connections (wire wrong) or improper voltage. If it is a low voltage relay please make sure the relay has the minimum voltage usually 24 volts. If it is below 24 volts the relay will chatter and burn up quick. I hope you can easily find and solve the problem. Steve Arnold

  47. hi Mr. Arnold,

    my grandmother has a fully self contained Bryant unit. The unit comes on, but doesn’t cool. it is 83°F in the house with the thermostat on 68°F. I don’t think it is froze up because there is water dripping as it normally should. The blades and motor are turning when it is on. can’t see the compressor or lines to see if they are overheating or freezing up because it is a one piece unit on the outside. she has never had this problem. she does keep allergen filters in the vents. I don’t know if that hurts the unit or not. are there any suggestions we could try before calling a repair tech. Thanks and have a blessed Memorial Day Weekend.

    1. Hi Mr. McMillan!
      I hope that you have a blessed Memorial Day as well! Thanks for your blessings and your question! I would not recommend using any filters in the supply lines because this can restrict air flow. It is OK to use the filters in the returns as long as they are not more than a Merv 11 filter rating. Some filters are so thick that they restrict air flow. I would like to suggest that you turn off the power to the unit then take the access panels off to see if the blower wheel, evaporator coil and condenser coils are dirty. See if the compressor is hot or warm on top. Most of the time when units do not cool properly it is because they are low on refrigerant charge and the only way to test is by the feel method or by using gauges. A unit that is low on charge will have a hot compressor. The suction line (larger line) should be cold like a cold coke can right out of the refrigerator if the unit is charged properly. I would also suggest checking the air flow and temperature of the air coming out of the registers. On an 83 degree indoor home you should be getting at 15 to 20 degree difference in the air coming out of the registers. So on an 83 degree indoor home temp you should get 63 to 68 degree air if the unit is working right. If not then you are probably low on charge or might have a dirty coil. Best of luck in finding and fixing the problem. God Bless you and your family today and Always!
      Steve Arnold,

  48. Hello, I have an Armstrong 3.5 ton unit which has served us well for 16 years. Now when she is fired up it will run for ~25 minutes or so then the fan shuts down. Called repair company, replaced capacitor and said fan was going bad. Replaced fan motor, new capacitor but you guessed it the fan still drops out. FYI, the compressor is still running. I bought a new contactor just because I didn’t want to make another trip.

    1. Hi Don! Sorry to hear that you are having the fan problem with your heat pump. I would like to suggest that when the fan motor cuts out, turn the power off to your unit, then touch the fan motor to see if it is running hot and going off on thermal over-load. If the fan motor is getting real hot, almost too hot to touch then you probably have a bad fan motor or a motor that is too small for your heat pump’s fan blade. Please make sure that the service company that installed the fan blade installed the correct motor and matching capacitor. If the motor is not getting hot and you think the defrost control is cutting the fan motor off then you might need a new defrost control. I hope you can easily find and fix the problem. I hope you have a blessed day. Steve Arnold

  49. Hello my question is my ac is running fine but the furnace came on the other day by it self the air was still working,I called the fire department because I never experienced any thing like that the fire department said thay never saw any thing like that,than the next day I called my ac repair man out two came and could not find any thing that would make the fire statt nothing burned but it was very strange.What do you think .Sin

    1. Hi! If this is a heat pump unit with supplemental electric heat and the heat comes on for no reason then you probably had a stuck sequencer, shorted thermostat wires or a thermostat problem. Most of the time when electric heat sticks on it is caused by a stuck sequencer. I have had customers that had over $500 bills when their sequencers were stuck. We sell sequencers on the following page: If you have a gas furnace where the heat comes on for now reason then this indicates a possible shorted thermostat wire or a thermostat problem. Best of luck in finding the problem. Steve Arnold

  50. Replaced contactor now Ac only turns on and off with breaker. Maybe I wired something wrong thanks

    1. Hi Thomas! Sorry to hear you are still having problems! One question that I would ask is are the contactor contacts closed with the unit running? If the contactor contacts are open with the unit running then I would say you have it wired wrong. If the contacts are closed (getting 24 to 28 volts AC to the contactor coil) with the thermostat calling for cooling to be OFF then you either have a bad thermostat or a shorted out thermostat wire. If you have the unit wired wrong then there should be a wiring diagram attached to the control panel door of your unit that you can use to check the wiring. Best of luck in finding the problem. Please email me at in you have any questions. Thanks! Steve Arnold

  51. Hi Arnold, I have a Arcoaire and the breaker was tripping. I replaced the breaker and I inspected the contactor because, it was cracked and the Positive wire was burnt with oxidation. I also replaced both capacitors and now I hear a click from the contactor making electricity with a solid connection but, nothing happens. The indoor fan will come on but, not the out door ac fan or compressor.

    Note* Before I replaced the circuit breaker. It would trip and I would reset it often. Thank goodness I replaced it because, it was running hot and it burnt the back of the breaker switch. 30 amp.

    Any help would be appreciated.



    1. Hi Mr. Silva!
      Most of the time when both the fan and compressor will not come on it is caused by (1) bad capacitors (2) improper or no voltage at the contactor. Please make sure you are getting 220 to 245 volts AC on L1 and L2 of your contactor, then with the contactor energized (24 volts at the coil) make sure you are getting 220 to 245 volt on T1 and T2 coming out of the contactor. (3) contactor not being energized 24 volts at the coil. We cover this problem in detail on the following page: We have an air conditioner troubleshooting flow chart on the following page: We have a long list of problems with answers on the following page: I hope you can easily find and fix the problem. Hope you have a great day! Steve Arnold

  52. The compressor on my unit tries to start and flips breaker even if the thermostat wires are unhooked. I replaced the contactor thinking that was the problem but it still does the same thing. Replaced the capacitor because it was bad, but still no difference. Do you have any suggestions?

    1. Hi Bradley! Thanks so much for the question. More than likely your compressor internal windings are grounded out. We discuss how to test for this on the following page: I would suggest that you turn off the power to your unit and inspect to make sure none of the wires are grounding out against each other. If you do not find any that are grounded out then you probably have a bad compressor and need either a new compressor or a new outdoor unit. Sorry. I hope it is not the compressor. Steve

  53. My outside unit keeps tripping the breaker. I changed the capacitor as it was getting weak and also changed the contractors as they where burnt. The unit stop tripping the breaker but the unit didn’t start until I pushed the contactor in by hand. The unit ran for a few minutes than tripped the breaker again do you have any suggestions. I checked the compressor with an ohm meter and it said it was good. The condenser fan motor the shaft is a little loose could the bearings be going out and shorting out the unit.

    1. Hi Ronda! Sorry to hear you are having problems with your unit tripping the breaker. Most of the time breakers are tripped due to a short to ground, from the compressor running too high of amperage or from a loose wire or bad breaker. If any of the wires are loose or if the breaker contacts are worn and pitted then this will cause arcing and will trip the breaker. We cover this problem on the following page: We also talk about this problem on the following page: I would suggest that you turn off the power to the unit and check to make sure all wire connections are good and tight. Since the contactor is not staying closed and you have to push it in with a screw driver to keep the unit running…your low pressure safety switch might be open. This could be cause by a low refrigerant condition. If your unit ran for a long time without the right refrigerant charge it might have over-heated the compressor, caused the windings in the compressor to melt down, contaminate the refrigeration system and cause your compressor to be tight. The only way to determine whether or not your compressor is tight would be to use an amprobe while the compressor is running. The amprobe will tell you how many amps the compressor is running. We sell an amprobe type meter on the following page: If you use the amprobe and see that the compressor is running over FLA (full load amps) then this would determine the compressor is tight and you need a new compressor. Normal running amps on a 3 ton AC would be somewhere between 12 and 20 amps depending on the efficiency of the unit. If you are running over 30 amps then this would mean that the compressor is tight. I hope that the problem is just a loose wire and not the compressor. Best of luck in finding and repairing your AC. God bless you and your family today and always! Steve

  54. Hello there, I have a York 3 ton unit. A wire grounded out and I blew the. I replaced it and it worked great. Few days later the transformer went out. Replaced it, worked great. Week later, tried using the air, no power. TransformER bad again. What can be causing me to blow transformers?

    1. Hi Brian! Thanks so much for asking this question! Sorry to hear you are having trouble with the transformers burning up often. Most of the time the cause of transformer burn out are low voltage thermostat wires grounding out, touching each other, or grounding out against the frame of the furnace or air conditioning unit. I would suggest that you inspect your low voltage thermostat wires thoroughly. I tried to cover this question on the following page: Most of the time a grounded out low voltage wire will blow the fuse on a control board if the board or furnace has a fuse. Best of luck in finding and fixing the problem. Steve

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