Posted on

Problem: My Air conditioner’s contactor will not engage. I am not getting 24 volts to the contactor to make it engage? What could be the problem?

Happy AC

Problem: My Air conditioner’s contactor will not engage. I am not getting 24 volts to the contactor to make it engage? What could be the problem?

Answer: If the contactor is not getting the 24 volts to the contactor coil then it could be a time delay relay (if the unit is equipped), thermostat problem, transformer problem, safety control, (low on refrigerate) wiring problem or a condensate pump, secondary drain pan safety switch problem. If you have a safety over-flow switch on your condensate pump or secondary drain pan then if you condensate pump is not working or if the secondary drain pan is full of water then this would cause the contactor to not get 24 volts to make it engage. I would suggest that if you do have a condensate pump that you check to make sure it is working.  I would also suggest that you turn off the power to the unit and check your connections to make sure all connections are good and tight. I would also suggest that you test the contactor with a volt meter to see if you are getting the needed 24 to 28 volts AC on the contactor coil. This could also be a blown fuse on your furnace or air handler control board. If the fuse on your control board is blown then you probably have a short in the thermostat wires or another control in the furnace or outdoor unit. This could also be a time delay relay problem. We sell a universal time delay relay on the following page: Please click here if you would like to see the time delay relay we sell. We sell transformers on the following page: Please click here if you are interested in seeing the low voltage transformers we sell.  Many air conditioners and heat pumps have low and high pressure safety switches on them to protect the unit from damage if the system pressure is too low  (low refrigerant charge) or too high (dirty outdoor unit or slow or bad condenser fan motor). If your unit is low on charge (I find most often) the safety switch will not allow the unit to start (contactor will not engage). You will need to call a service tech in order to check the charge on your unit. We sell contactors on the following page: Please click here if you are interested in seeing the contactors we sell. Please send us your unit’s model number if you would like for us to find out and see which OEM contactor or parts your unit requires. Our email address is: support@arnoldservice.com  Below we have a real informative YouTube video made by grayfurnace man which show how to troubleshoot and test a contactor. We have other troubleshooting links on the following page: Please click here if you would like to see our other troubleshooting pages. If you have any questions we will be glad to answer them. Please email us: support@arnoldservice.com or comment in our comments section below. We would love to help you out and have your business!

79 thoughts on “Problem: My Air conditioner’s contactor will not engage. I am not getting 24 volts to the contactor to make it engage? What could be the problem?

  1. I have a Trane 20i 4TTZ0/4TWZ0 I had to replace the HP contactor, the new one is chattering this is in the heating mode. The ambient air temp on the thermostat drops to -18 degr. when compressor is running then returns to normal ambient outside temp. when comp shuts down?

    1. Hi! If your contactor is chattering then this is a sign that the low voltage to the contactor coil is not high enough. You should be getting a minimum of 24 volts AC to the contactor coil. If your aren’t getting 24 volts then you might have a weak transformer, weak batteries in your thermostat or a short or loose connection in the thermostat wires on controls. If the contactor is chattering then this is really hard on the contactor and compressor. I have had contactors burn out in a matter of minutes when they chattered. I hope that you can find and fix the problem.

  2. Hello.
    I couldn’t find problem either, but when I went to attic and checked panel under the unit to collect water if my discharge pipe gets clogged, I found it full of water. So, my overflow sensor disconnect power to compressor. I vacuum water out and try to turn on AC on. Everything worked perfectly.
    My question: why water got to panel under the unit even water was dripping heavily from the discharge pipe?

    1. Hi Marius! Thanks so much for telling me how you fixed your air conditioner problem by cleaning the water out of your secondary drain pan which allowed the secondary drain pan safety switch to close and start the air conditioner up again! Problem fixed! I will add this to the list of problems to check for in the post above. Thanks! Water in the secondary drain pan usually indicate that either the condensate drain line is stopped up or you have a leak in the evaporator coil drain pan. Most of the time the problem is in the condensate drain line and using compressed air or a wet vac to suck the junk out of the drain line that is causing the stoppage usually eliminates the problem. If cleaning the condensate drain line does not solve the problem then you might have a rusted through evaporator coil drain pan and this would indicate the need for a new drain pan or new evaporator coil. I hope all the problem is the condensate drain line stopped up. Evaporator coil replacement is expensive. Thanks for your comment! Steve

  3. Hi, My inside unit comes on when the thermostat is set to cool , that seems to be fine, BUT my outside fan will not come on at all and no sound, so I replaced the capacitor and turned on the inside unit but the fan outside unit turned on a split second and shut off immediately. I then bought a contactor and installed that ,then tried and set thermostat to cool again and again it came on fine but no movement or sound from the outside unit. It is a Nordek and I do not see a control board or a relay switch at all. I would appreciate any advise ,Thankyou
    Richard

    1. Hi Richard! I am assuming that you can not get 24 volts to the contactor coil to get the contactor it engage. I would suggest that you get an insulated screw driver so there is not chance that you get shocked and push in on the contactor’s contacts to see if your unit will start. If you can not get the contactor to engage without manually pushing the contacts down that you either have a thermostat problem, thermostat wire problem (possible broken or loose wire), high or low pressure safety switch problem, time delay relay problem (if equipped), low voltage fuse blown problem, if this is a heat pump it could be a defrost control board problem or a low voltage transformer problem. Since the indoor air handler works then I would not think you have a transformer problem. With the thermostat calling for cooling you should have 24 to 28 volts between the Y and C terminals to energize the outdoor contactor. If you do not have 24 volts between Y and C then you either have a thermostat problem or a broken thermostat wire problem. You would need to keep checking for 24 volts between the Y and C wires. Where you stop getting the 24 volts is where the problem is located. If you have anymore questions please let me know. I hope you can easily find and fix the problem. Steve

      1. Hello, I have same problem as well. When I push button in the Trane contactor, fan will start moving, when I release button fan will stop moving. Can’t find the problem.
        Thanks

      2. Hi Marius!
        Sounds like since you can not get the contactor to engage without manually pushing the contacts down that you either have a thermostat problem, thermostat wire problem (possible broken or loose wire), high or low pressure safety switch problem, time delay relay problem (if equipped), low voltage fuse blown problem, if this is a heat pump it could be a defrost control board problem or a low voltage transformer problem. I would suggest that you start testing with a volt meter between R and C you should have 24 to 28 volts. If not you have a transformer or broken wire problem. With the thermostat calling for cooling you should have 24 to 28 volts between the Y and C terminals to energize the outdoor contactor. If you do not have 24 volts between Y and C then you either have a thermostat problem or a broken thermostat wire problem. We have a post about this problem on the following page: https://arnoldservice.com/problem-my-air-conditioners-contactor-will-not-engage-i-am-not-getting-24-volts-to-the-contactor-to-make-it-engage-what-could-be-the-problem/ You would need to keep checking for 24 volts between the Y and C wires. Where you stop getting the 24 volts is where the problem is located. I hope you can easily find and fix the problem.
        Steve

      3. Hello,
        Today I had an AC guy. He checked the power by pass thermostat. Fan inside and heat was working, but AC not. He told me the problem inside the unit, because power comes from thermostat to unit, but does not from unit to the compressor.
        He told me my unit needs to be rewire. Really? It less then two years old.
        Please, advise.
        Thank you so much for helping community.

      4. Hi Marius! Sorry to hear that your air conditioner is not working and your AC service guy says the unit needs to be rewired. The only reason why your unit would need to be rewired would be if you have loose and burnt wires inside your unit. If your contactor is not getting 24 volts to make it work or energize then I would suggest that you do the testing like in the above post’s Youtube video. I would check and see if you can get the unit to come on by holding down the contactor contacts with an insulated screw driver. If you can not get the contactor to engage without manually pushing the contacts down that you either have a thermostat problem, thermostat wire problem (possible broken or loose wire), high or low pressure safety switch problem, time delay relay problem (if equipped), low voltage fuse blown problem, if this is a heat pump it could be a defrost control board problem or a low voltage transformer problem. I would suggest that you start testing with a volt meter between R and C you should have 24 to 28 volts. If not you have a transformer or broken wire problem. With the thermostat calling for cooling you should have 24 to 28 volts between the Y and C terminals to energize the outdoor contactor. If you do not have 24 volts between Y and C then you either have a thermostat problem or a broken thermostat wire problem. We have a post about this problem on the following page: https://arnoldservice.com/problem-the-air-conditioner-outdoor-unit-will-not-come-on/ You would need to keep checking for 24 volts between the Y and C wires. Where you stop getting the 24 volts is where the problem is located. I hope you can easily find and fix the problem. Steve

  4. How can I detect if the cause of the problem is low pressures ( refrigerant charge ) and not someting like short circuits or other thing? without measuring the pressure is it possible to find out for sure that the safety control is the reason I dont have 24 on my contractors ?

    1. Hi Al! Without gauges it is a guess. If I did not have guauges I would turn both the high voltage and low voltage power off to your unit, cut the two wires that go into the low pressure switch, strip the wires back and join the two wires together with a wire nut. Make sure that you leave enough wires sticking out of the low pressure switch so you can reattach the wires after this test. If it is a low pressure switch problem then the unit’s contactor will be energized and you will know that you are low on refrigerant charge. Since it sounds like you have a volt meter I would start testing where the 24 volts comes into your unit from the thermostat. It should be two wires if you have a regular AC system. Test with your volt meter until you stop getting 24 volts. Where the 24 volts stops then this is where your problem is. I hope you can easily find and fix the problem. Steve

  5. Hey Steve. When I turned the air on for the season I noticed that it wasn’t cooling off my building. An AC repairman came out and put in freon and replaced the contactor. Now the air works sometimes and sometimes it doesn’t. The circuit breaker for the air handler has tripped. Or the contactor isn’t turning on the compressor causing it to overheat. Do you have any thoughts about what could be wrong? Thanks

    1. Hi Larry! Since the circuit breaker in your air handler is tripping I would think that you either have a short to ground in your air handler or a circuit breaker that is arcing and needs to be replaced. I would suggest that you turn off the power to the air handler and make sure all wire connections are good and tight. Inspect the air handler for shorted or burnt wires and replace the wires if you see they are burnt. If the air handler is blowing the breaker and shutting off then this shuts off the low voltage transformer and could cause you to to not have power to any of your system’s low voltage controls. It would depend on how they wired the air handler, but I have seen where the outdoor unit’s circuit breaker is housed on the air handler. If your outdoor unit is blowing the breaker over time then you could have a loose wire, a dirty outdoor unit, a restriction in the unit’s refrigeration cycle, an outdoor fan motor that is shutting off (you said the outdoor unit was hot. If the fan motor is not running this would make the outdoor unit hot). This could be a weak run capacitor problem if your outdoor unit’s capacitor is weak. We have lots of air conditioning and heat pump troubleshooting questions with answers and Youtube videos on the following page: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-questions-answers-index/ We also have an air conditioning and heat pump troubleshooting simplified page that I hope will help you find and fix the problem: https://arnoldservice.com/air-conditioning-heat-pump-troubleshooting-simplified/ We also have lots of troubleshooting advice on the following page: https://arnoldservice.com/troubleshooting/ If you have any specific questions please let me know. I hope you have a great day! Steve

  6. This is in regarding of June 12, 2018’s post from Steve and Joshua.

    Hi Steve,
    I had replaced all the components on the condenser and compressor unit except the compressor as mentioned in my original post. I also mentioned that I manually pushed contactor to close, and that would make condenser fan to be on, but not compressor. I believe it must have to do with low freon. I followed your instruction and found the low freon pressure switch inside condenser. It was tripped. Since I don’t have a freon pressure meter, I called a local A/C service to check it out for me. The technician came out and confirmed it was the low freon problem that triggered the low pressure switch to be tripped and prevented compressor from coming on. The assessment is to replace the whole AC heatpump due to its severe leaking and aging (19 years old). We looked at my neighbor’s 30 years old Bryant heatpumps and they are still going strong. However I don’t have good experience with Carrier either. The Goodman heatpump is one of the worst. My next heatpump will be Trane I guess.

    1. Hi Joshua! Sorry that you have to get a new heat pump. Yes, I like Trane heat pumps the best. Steve

  7. Hello Steve, Thanks big-time for sharing your knowledge and troubleshooting tips. I found your site very helpful solving an issue with my central AC. Lack of 24 volts to the contactor was the key. What surprised me was that the failure was due to a thermo-time switch in the propane furnace evacuation fan. I was not aware that this part of the furnace would affect the AC. (Additionally the furnace had not been used for heat for months. The compressor just failed to come on one day, even though the blower in the air handler was circulating air.) Thanks again for the clues to solve my problem.

    1. Thanks so much for taking your time to post the solution to your problem with the contactor not getting 24 volts! I would have never guessed to test the thermo-time switch! I hope that your post and comment will help others in troubleshooting and fixing their air conditioners! God bless you and your family today and always! Steve

  8. Dear Mr. Arnold,

    I have a home generator specifically wired to a air handler along with other esential items in the house when I have a power disruption. My problem is that everything works except the air handler. We are getting power to the unit and the generator is shown that it is receiving the appropriate voltage but the unit just engages and the disengages repeatedly, on then off, on then off. The AC contractor says the generator is the problem, the generator contractor says there is a problem with the air handler. Could you possible diagnose this situation. At wits end! Thank you.

    1. This sounds like a generator problem where the generator is not producing enough voltage (amps) to start the motor. The simple test would be if the motor works fine with your normal power on and not with the generator power on then this wold be the generator’s fault for sure. I would suggest making sure that the motor capacitor is in good shape and your generator is producing a minimum of 110 volts. Motors usually have a long amp draw for a split second at start up and if the voltage is dropping too much the motor will act like you describe. You might have to turn up the rpm on your generator to adjust to the extended amp draw during start up. I hope you can easily solve this problem. Steve

  9. My heat will not cut off after it has reached the set temperature i have set the thermostat at. Even when i cut off the unit by using the thermostat heat continues to blow from my vents. Lots of it. I try turning on the AC and nothing but heat continues to run. Only way to make it stop is by cutting off the unit by the breakers. What could be the problem?

    1. Hi Ben! This sounds like you probably have a short in the thermostat wires which is causing the heat to run all the time. If the Red and white thermostat wires are shorted together then the heat will run all the time. I would suggest that you examine your thermostat wires to see if they are shorted any where. I would pay close attention to where the wires go into the body of the furnace. Many times the wires will short against the frame of the furnace. This could also be a thermostat problem or a stuck gas valve relay on the control board. I would suggest that you remove the white (W) wire from the thermostat. If the heat stops then more than likely it is a thermostat problem. If the heat continues with the W removed then you probably have a shorted thermostat wire, stuck control board gas valve relay or gas valve that is stuck open. This can be dangerous so please be careful. I hope you can easily find and fix the problem. Steve

  10. Hi Steve,
    First I would like to thank you for taking the time to help us all. My A/C unit cools great and the furnace is hot also. My question to you is this. My wife and I just purchased our first family home everything seems to work as it should except the fact that when everything’s off my blower is still circulating air “all the time” so while the kids were down for their nap today I pulled the unit cover off and checked the fuses with my multimeter. They were good and checked voltage on the contactor I have voltage on both top and bottom, but I can’t seem to find 24-28 volts on either side post. Am I headed in the right direction and where should I go from here it’s a 2013 Carrier unit it has the furnace built in.

    1. Hi Mr. McConnell! Thank you so very much for your kind words. I believe that your problem is that your blower fan runs all the time even when the heat and air conditioner is turned off. It sounds like you have what they call a packaged unit where both the air conditioner and furnace is housed in one packaged unit, which sits outside your home. The contactor that you are referring to in your question, most of the time controls the air conditioning part of your system and not the fan blower. The contactor normally cuts the compressor and outdoor fan on when the thermostat calls for cooling. We have a post about the problem where the fan runs all the time on the following page: https://arnoldservice.com/problem-your-fan-on-your-furnace-runs-all-the-time-and-will-not-shut-off/ I hope this will help you out. If you have any other questions please let me know. I hope you have a great weekend! Steve

  11. Had an ecobee3 on my upstairs a/c-heater. One day last week the a/c was not on and the ecobee was blank and clicking. Thinking that the thermostat was not working, I hooked up my old battery operated thermostat. The system started working and it works normally with the old thermostat. I checked the fuse on the furnace board and it is fine. I hooked the ecobee up to the upstairs unit and it works fine there. I am confused to why the system works with the old thermostat. Since it is working wouldn’t it indicate that there is 24 volts in the r wire?

    1. Hi Joe! I really do not know about the wiring directions for the Ecobee3 thermostat. If the Ecobbe requires a 5 wire wire hook-up with a common wire then your 4 wire system will not work with the Ecobbe. If the Ecobbe requires only 4 wires to work properly then you might not have a strong enough transformer to power the Ecobbe thermostat. You might need a higher VA transformer. Most transformers are 40 VA and you might need a 50 or 60 VA to power the thermostat. Sorry, I am just guessing. You might want to contact Ecobbe support and ask them. Steve

      1. Thanks for the response and help Steve. The ecobee3 does require a c-wire. And it was working beautifully until last week. I don’t have any voltage from r to c at the thermostat which seems to me is why the ecobee3 isn’t working. I’m not totally clear about how the older battery powered thermostat works, but if it runs the system, wouldn’t that require and indicate that there is 24-28 volts in the r wire or does the thermostat just make connections between the appropriate wires to activate other equipment to start either heat or a/c without the need for the voltage? I hope my question is clear.

      2. Hi Joe! Your furnace’s low voltage transformer should supply 24 to 28 volts AC between the R and C thermostat wires both at your furnace control board and your thermostat. If it is not doing that then you either have a bad transformer or a broken thermostat wire. I have had questions asked about the Ecobee thermostat before and the problem was with the low voltage transformer not being strong enough. Need a higher VA transformer. Your old thermostat has it power through the batteries for controlling thermostat functions (switching the relays inside the thermostat). Yes, the R (Red) wire should be hot going to your old and new thermostat. It is impossible to test the R (Red) wire by itself without a C (Com) because electricity always travels to C (com) ground or neutral. I would suggest checking to see if you get 24 volts between R and C with the wires disconnected from the Ecobee thermostat. If you are not getting the 24 volts then you either have a bad transformer of a broken thermostat wire. If you are getting 24 volts then the thermostat is taking too much load or voltage from your furnace’s transformer and you need a bigger transformer. I hope you can easily find and fix the problem. Steve

  12. My blower is not working. My Air conditioner only comes on if I do it manually if I release it it goes off. Not real electrical. But can follow instructions if not in jargan

    1. This sounds like you are not getting 24 volts to the contactor or the furnace control board. Will anything on the furnace or AC work. If nothing works I would check with a volt meter set to “Volts AC” and test L1 to a neutral on the control board to make sure you are getting 110 volts to the control board. You might have to tape the furnace door safety switch closed so you can do testing. I would also recommend testing between R and C (com). You should be getting 24 volts between R and C and with the thermostat calling for cooling you should get 24 volts AC between Y and C and G and C. Y sends 24 volts to the AC’s contactor. G sends 24 volts to the blower relay on the control board. If your control board has a fuse then I would recommend checking to make sure the fuse is good. I hope you can easily find and fix the problem. Steve

  13. Hi, We have what is “i think” a 1999 3-Ton Goodman Outdoor AC Unit. A few weeks back, the unit was making some rather loud screeching sounds. I just it off and decided it was most likely the Blower Motor had gone bad. It was no longer spinning. So, I ordered the Exact same blower motor. In the meantime, I used a box fan facing upward and ran that to continue to use the AC unit while we waited for the part. I know, it was not the best choice and could break more. Long story short, the Box fan overheated and stopped working during the middle of the night. I noticed it about a half hour later and turned off the AC unit. I feared I had done some major damage. Thought I was going to have to buy a whole new unit.

    We had a HVAC tech (friend of mine) come out and look at it the same day the Blower Motor arrived. He told me that the Unit was in fairly good shape and that we wouldn’t need to replace it. He said, “he could fix this one”. So, he installed the Blower Motor and told me that it was fixed. I didn’t quite believe him but decided to give it the evening to see if it would cool down. Sure enough, it didn’t. He also told me that the Refrigerant was at 3/4 full, how he knows this or measured it is beyond me as I didn’t see him check this.

    So, I ordered a New Aerovox 40-5uF 370VAC Motor Start Capacitor Z64P3745W, the exact same capacitor that was already installed (I took the part numbers directly from the installed parts). A week went by and I received the part. I installed it. AC unit still did not produce cold air. So, I ordered the 24 volt 1 Single Pole Contactor Relay B13603-21 3100-15Q179 and I just received this today. I installed it. Now, the AC unit still does not seem to be cooling. I’ve checked the wires running into the Compressor and they seem to be in good condition. The blower motor definitely turns on. The exterior fan is running, but I don’t hear the compressor kick on and give that low humming sound. The inside fan blows fine. The Thermostat is working properly. So, I’m leaning towards the compressor but I’m a bit frustrated that replacing the blower motor, capacitor and contactor relay hasn’t solved this.

    At this point, I’m assuming the compressor will need to be assessed. I’m leaning towards calling an HVAC tech, from a company, to diagnose it, but I’ve been trying to troubleshoot it myself, to save money. Any meaningful, or productive suggestions or guidance is welcome, thanks,

    1. Hi Marshall! Sorry to hear that you have tried many things without getting any cool air to come out of your air conditioning system. As you described it sounds like the compressor is not coming on. This could be a locked up compressor, a compressor where the windings are broken and burnt out, a loose or broken wire or a compressor that is not wired right and not getting the voltage to start. We have a page where we discuss some of these problems: https://arnoldservice.com/problem-compressor-will-not-run/ I would suggest feeling the top of the compressor to see if the compressor is hot. If the compressor is hot then this means that the compressor is trying to start, but has probably gone off on internal thermal over-load. If the compressor is trying to start and can’t then I would suggest trying a compressor hard start booster. We talk about this problem on the following page: https://arnoldservice.com/problem-air-conditioner-compressor-will-not-start/ If your unit is low on refrigerant charge like your service person said then most units will not cool properly and over time running low on refrigerant can damage a compressor by making it over-heat. I would suggest that you get the unit charged up properly if you can get the compressor running. I would suggest making sure that you are getting 220 to 245 volts AC on both sides of the contactor when your thermostat is calling for cooling. The top of the contactor should be labeled: L1, L2, T1 and T2. You should be getting between 220 to 245 volts between L1 and L2 and with the contactor energized, you should get 220 volts between T1 and T1. I would also suggest that you look at the wiring diagram that should be inside the unit and make sure the compressor is wired according to the wiring diagram. I hope you can easily find and fix the problem. Steve

      1. The outside unit’s condenser fan and compressor are not coming on at all.

        Hi Steve, I really like your webpage discussion about HVAC. your forum makes me want to try DO-It-Yourself on my AC. I have a 1999 Goodman Heatpump Model CPKJ30-1AB. I believe it’s a 2.5 Tonage heatpump. My problem is that the compressor is not coming on. I have two exact same type of units, one for upstairs and one for downstairs. Right now the downstairs unit is not working. When I set the thermostat to cool, it only blow the warm air from the air blower in the attic. The outside unit’s condenser fan and compressor are not coming on at all. I get 245 volts on the inputs of the contactor , but not the 24 Volts. I get 27 volts coming from the transformer and to the defrost board. I do not get 27 volts from defrost board to the coil of the contactor. If I pushed the switch on the contactor to manually make connection, the condenser fan will turn on, but not compressor. The top of the compressor is cold, no matter how long I held the contactor switch on. The following are the things that I tried.
        1. I am getting 245 volts on the contactor.
        2. I am getting 27 volts between R and C wires behind the thermostat and on the control panel feeding into the defrost board on outside unit.
        3. I am not getting 27 volts coming out of the defrost board to the coil of the contactor.
        4. I swapped thermostat and the outdoor control panel (defrost control board, defrost thermal couple, contactor, motor starting cap), and the condenser fan from a working upstairs unit to the non-working downstairs unit. The upstairs unit is still working, but the downstairs is not. So the components on the outdoor control panel are all good (defrost control board, defrost thermal couple, contactor, motor starting cap).
        5. During parts swapping, I also measured the compressor windings and they are not open nor shorted to ground. The resistance from R-C is 0.8 Ohms, S-C is 2.3 Ohms , and R-S is 3.1 Ohms, right on the money.
        6. I went to the attic and opened the air handler, I only saw transformer and a bunch of wires. Not any switching sort of thing for me to flip or try.

        I am running out of ideas, I would like to borrow your brain on this. Thanks, Josh

      2. Hi Joshua! Thanks so much for your kind words! Glad we have motivated you to try and Do-it-yourself! Sounds like you pretty much have the problem figured out with not getting 24 volts to the contactor coil. You just need to see where the 24 volts stops and that is where the problem is. You should have 24 to 28 volts AC between the Y (yellow thermostat wire) and C (com thermostat) wires coming from your thermostat and going into your outdoor unit. If you are getting 24 volts out of the yellow wire going into the defrost board and nothing coming out of the defrost board to the contactor then I would think that you have a problem with your defrost board or another low voltage control. Maybe the contactor has a short and is robbing the voltage going to it. I would suggest that you unplug the contactor and see if you get 24 volts through the wires. You might try to wire directly to the contactor through the Y and C to get the contactor to close. Maybe the reversing valve solenoid that is energized through the “O” connection is robbing the voltage. The solenoid is energized all the time in the cooling mode on Goodman heat pumps. I see from our Goodman program that your unit does have a low pressure switch. If your unit is a little low on refrigerant the low pressure switch will not allow power to the contactor. If you want a parts list please email me and I will be glad to send it to you. I hope you can easily find and fix the problem. Steve

  14. Hi, Steve! I could use your knowledge at this moment and thanks for your time in answering mine and everyone else questions. My name is Josh and am trying to fix my parents AC which is not cooling the house at all after I put in a new capacitor and nothing is happening. The fan is spinning just fine. I don’t hear the compressor coming on. What can this be?

    1. Hi Josh! Sorry to hear that your parent’s air conditioner is not working. Thank you so very much for your kind words! Since you say that the fan is running and the compressor is not….I would suggest that your read the following information that we have posted on the following page: https://arnoldservice.com/problem-compressor-will-not-run/ I hope that you can easily find and fix the problem. If you have any other questions please ask anytime. Steve

  15. Hi Steve, excellent site and it’s awesome to see that you’re answering questions currently.
    I have an old Nordyne heat pump system where the outside unit is not coming on now. This just started two days ago and it was working beautifully just before this issue.
    I am getting 24v to the outside unit on the Y and C terminals. The Y terminal feeds straight to the T1 terminal on the defrost control board. But, I am not getting 24v going to my contactor that comes out of the T2 terminal to the contactor. It looks like there is a time delay circuit it goes through on the board, but even after the 5 minutes, it still does not energize the contactor. Would this be a delay problem with the board or could it still a low refrigerant problem? I should add that when I bypass T2 and jump to the contactor from Y the unit runs seemingly normal. The refrigerant line starts sweating and my laser thermometer reads 65 degrees when pointed at the copper line.
    https://drive.google.com/file/d/0BwfZk9oPZtMEM0liRXFPUFNxams/view?usp=drivesdk

    1. Hi Tim!
      After reading your description on what you have tried and after looking at the wiring diagram to me it looks like you have a defrost control board problem since you can by-pass the defrost control and the heat pump runs properly. I would suggest trying a new defrost control board with new defrost thermostats. I am sorry, but we do not sell any Nordyne defrost control boards. I hope you have a great day and weekend! Steve

  16. My contactor is not engaged. I do not know yet if I have any voltage out there or not. I do know that when I push it in the unit comes on and after three or four minutes the large copper line starts to frost. The blower motor in the attic will not come on. If I tested correctly, I have 26 volts coming out of transformer. My question is why won’t the blower come on? There is a fuse on the board which is good. There is a staus light that is on. I turned the thermostat to fan only and calling for cooling. What should be my next step?

    1. Hi Greg! I would make sure that you are getting 24 to 28 volts AC to your control board from your thermostat. If your thermostat has batteries, I recommend making sure they are in good shape. The thermostat controls the 24 volts to start the fan and outdoor contactor that makes the outdoor unit come on. I am sorry you will probably have to go in the attic to do some testing. You might have to tape the furnace blower door safety switch shut so you can do testing with the electricity on. With the thermostat set to call for cooling (AC running) You should be reading 24 to 28 volts AC between terminals R and C, terminals Y and C and terminals G and C. If you do not get 24 volts between these terminals then you have either a thermostat problem or a broken thermostat wire problem. The blower should be running and the outdoor unit should be running if you get 24 volts between those terminals. If you are getting 24 volts between those terminals and the blower is not running then you might have a control board problem or a blower motor problem. Please make sure the blower motor capacitor is in good shape. If you have any other questions please let me know. I hope you can easily find and fix the problem. Steve

  17. First I would like to say that this an amazing site with a lot of great information, thank you for all of the help that you provide here. My problem is a little baffling to me and I was hoping to find out if I’m going the right route. My ac won’t come on outside , no fan or condenser noise. If I push the contactor in , the ac will engage but only as long as I hold it in (the contactor is clean, and relatively new). I am getting 250v coming into the ac, from the house, I have 24v going into the short cycle time relay but not coming out at the contactor to pull it in. Therefore I am thinking it might be the relay that needs to be replaced? Any ideas would be greatly appreciated ..

    1. Hi Mike! Thank you so very much for your kind words! It sounds like you are on the right track by suspecting the time delay relay as the problem. You should be able to temporarily wire around the relay so the 24 volt wires go directly to the contactor to make sure the relay is at fault. Most time delay relays are used on scroll compressors to prevent the scroll from running backwards during a power outage. If you need me to look up parts then please send me your make and model number to me at: arnoldservice@gmail.com. I hope you can easily find and fix the problem. Steve

  18. So my contactor will not pull in, won’t even let me jump it on from the board. Replaced transformer and thermostat. Wiring is good. Bad board maybe? Problem code is blinking normal code

    1. Hi Dante! I do not know if you are referring to a defrost board or a time delay board on the outdoor unit, or the furnace control board. Most furnace control boards do not usually have anything to do with the contactor getting 24 volts other than the board is used as a junction between the “Y” wire and the “C” common wire on the control board coming from the thermostat and going out to the outdoor unit. I would suggest turning your thermostat down so the AC comes on, then trace the 24 volts down (Y and C) wires with a volt meter and where you quit getting 24 volts volts then this is where the problem is. If the contactor is getting 24 volts and not pulling down then you probably have a bad contactor coil and you will need a new contactor. We sell contactors on the following page: https://arnoldservice.com/product-category/air-conditioner-parts/ac-contactors-heat-pump-contactors/ I hope you can easily find and fix the problem. Steve

  19. hello i just replaced my condenser fan motor and i wired it the right way. the issue is that when i put the fuses back in the disconnect box the fan motor runs then it stops, then turns on again for like a couple of seconds then turns back on again i notice that my contactor keeps coming on and off. please help me and find out the solution i gladly appreciate your help

    1. Hi Anthony! It sounds like the problem is not the fan motor, but something is causing the contactor to go Off and ON. Most of the time when I was doing service work this short cycling of the condensing unit was caused by the system being low on refrigerant charge or as most people say, “low on Freon”. If you do not have enough refrigerant in your unit the compressor starts up and because it does not have enough refrigerant the low pressure side is reduced to the point where the low pressure safety switch senses the low pressure and the low pressure switch turns the unit off. After the unit is off for a short while the low pressure safety switch closes and the unit comes back on. This ON and Off cycle will continue until the unit is charged up with enough refrigerant. I would suggest that you have your refrigerant charge checked out to make sure it is charged up properly. Another thing that might cause this would that the batteries (if equipped) in the thermostat might be weak. Please make sure that your batteries are in good shape if you have a thermostat with batteries. There are many other things that might cause the contactor to not engage. These are discussed in the post I wrote above. I hope you can easily find and fix the problem. Steve

  20. I have 27 volts on t-stat wires coming from board to outside when disconnected from contactor coil. When I connect wires to contactor coil I’m getting 0 volts across the coil which results in the contactor not being energized. What could be causing this problem?

    1. Hi! You might have a short to ground in the contactor coil which is causing the voltage to go to “0”. This could also be caused by a loose thermostat wire or a thermostat that is going bad. When the load on the thermostat is applied the relay inside the thermostat can not handle it and the volt goes to “0”. I would suggest that you check all thermostat wire connections to make sure they are tight. I hope you can easily find and fix the problem. Steve

  21. Heating and fan are fine. But when A/C is on, thermostat has no display and 5A fuse was blown. But after fuse is replaced, same issue happens again. Heating and fan work fine, but when A/C is on, thermostat has no display.

    1. Hi Bill! Most of the time when the fuse blows on the control board when the AC is turned on it is caused by a short to ground in the thermostat wires that go to the outdoor unit. Many times I have found where animals have chewed through the insulation on the wires and caused them to short out. I have also seen where sun deterioration has messed up the insulation and where the wires are pinched where they exit the furnace or enter the AC unit has caused a short. I would suggest inspecting your thermostat wires to make sure they are in good shape. I have also seen blown fuses on the control board caused by controls like where the contactor coil or reversing valve solenoid have shorted out and caused the fuse to blow. I would suggest checking your thermostat wires and if you do not find any problem with the wires then check the coil on the contactor to make sure it is not grounding out. I hope you can easily find and fix the problem.

  22. Hi there, I have been narrowing my issue down for about a week now. My fan inside comes on, but no cold air. The furnace works fine.

    At this point, here is what I know: my contactor will not engage, but when depressed manually the unit runs fine. I am getting 240V high voltage to the contactor, but not 24V across the coil when cooling is called. On the board, I get 24V between C and Y when the thermostat calls for cooling.

    the control board is 1012-925C, amazon link:
    https://smile.amazon.com/1012-925C-Rheem-Replacement-Furnace-Control/dp/B00FYWHD54/ref=pd_sbs_328_3?_encoding=UTF8&psc=1&refRID=C01CA6HZYCEMVEXB1TN0

    I am getting 24V from the transformer going to the board at COM (bottom center of board, next to the 9-pin).

    Not sure what to try next.

    1. Hi Blake! I would think that something is wrong with the control board or where the 24 volts stops. I would suggest testing the Y and C wires as they come into your outdoor unit. Where you stop getting the 24 volts then this is where the problem is. I would also check to see if you have low refrigerant (low pressure) or high pressure safety switches on your unit. If one of these are open then this would cause the contactor to not close. Some compressor have thermal switches on the top and if they are open or bad this can cause the contactor not to open. There are lots of safety controls on the units that can cause the contactor not to close. You will need to troubleshoot with a volt meter. Sorry that I can not be of more help. Steve

    2. My contactor is out and when I push it in the condenser unit comes on what is the problem

      1. This sounds like you are not getting 24 volts to the contactor coil to energize the contactor. We discuss what the problem could be in the “Answer” above. You would need to test with a volt meter and see where the 24 volts stops then this is where the problem is. I would start by turning the thermostat down so the thermostat is calling for cooling. Then test with a volt meter starting at the furnace control board testing thermostat wires, between Y (usually yellow wire) and C (common, usually blue wire) and see if you are getting 24 volts. If you aren’t then you have a thermostat problem or thermostat wire problem. If your thermostat has batteries please make sure they are in good batteries. If you are getting 24 volts between Y and C at the furnace control board then proceed outside and continue to test. Where you stop getting 24 volts stops is where the problem is. You might have a bad contactor coil if you are getting 24 volts to the contactor and it is not pulling down. We sell contactors on the following page: https://arnoldservice.com/product-category/air-conditioner-parts/ac-contactors-heat-pump-contactors/ I hope you can easily find and fix the problem. Steve

  23. My AC unit is cycling on 2 seconds off a few seconds. I pulled the cover and manually depressed the contactors. The unit comes on and stays on as long as I have the contactors depressed. I had the unit charged a summer or two ago and wonder if my freon is too low. Could it be anything else? I’d like to check everything possible before I call a technician out. Thanks much, Brett

    1. Hi Mr. Butler! This sounds like a low pressure switch problem and you might be low on refrigerant or have a blockage in the refrigeration system. This could also be caused by a weak battery in the thermostat. If your thermostat has batteries I would recommend making sure they are in good shape. If you do not have manifold guages to test the refrigerant level then you will probably need a tech to check out your system. I hope you have a great day! Steve

  24. WHEN I JUMO THE RED AND YELLOW POLES ON MY THERMOSTAT THE CONTACTOR ENGAGES BUT WHEN I PUT IN THE NEW THERMOSTAT THE CONTACTOR WILL NOT ENGAGE

    1. This sounds like you have a thermostat problem. If the red wire is attached to “R” on the thermostat and the yellow wire attached to the “Y” on the thermostat and you turn the thermostat to cool, turn the thermostat way down then the AC unit’s contactor should come on. I hope you can find the problem. Sounds like a faulty thermostat. Steve

  25. i have payne heat pump. that was installed in aug.2016 its not working, its is getting 24 volts to the outside, but not getting power to the circuit board to the contactor

    1. Hi Selina! Please check to make sure that the circuit breaker has not tripped. Even though the breaker looks OK I would suggest turning it all the way off and back on again. If this does not fix the problem, then I would suggest calling the company that installed the heat pump. Heat pumps with the electronics can be pretty complex. You new heat pump should be under warranty since it was just installed last year. I hope you can get your heat pump fixed soon. Steve

    2. Safety switch engaged if freon is too low

      1. Hi! A low pressure safety switch on the outdoor condensing unit that is open (showing low on refrigerant) can be one of the causes of why a contactor will not engage. If your low pressure safety switch is closed then this is not the problem and I would suggest looking for other problems like broken thermostat wires, thermostat problem or a bad contactor. If you are getting 24 to 28 volts AC to the contactor coil and it is not closing then you have a bad contactor. I hope you can find and fix the problem soon! Steve

  26. My contact only works when I push the switch in the middle exchange contactor and capacitor what could be the problem

    1. Hi Mr. Jones! You would need to test and see if you are getting 24 volts AC to the contactor coil when your thermostat is calling for cooling. If you aren’t please go through testing the various components to see why you are not getting 24 volts to the coil. We discuss this in the post above. I would start with testing to see if you are getting 24 to 28 volts between the C (com) and Y (yellow) terminals on your control board when the thermostat is calling for cooling. If you aren’t then you have a thermostat or thermostat wire problem. Continue on out to your outdoor unit. Where you stop reading 24 to 28 volts then this is where your problem is. Best of luck in finding and fixing your problem. Steve

  27. i have no 24 volts at the condensor. i have 24 volts from the thermostat and no 24 volts out of the board. i have 24 volts at the transformer. i believe the only thing in between would be the board? or am i missing something

    1. Hi Charlie! The low voltage transformer should be directly connected to the control board through the R and C (com) terminals on the board. If you have a blown fuse on the control board then you might not get 24 volts between R and C. I would suggest checking the low voltage fuse on the control board if you have one. If would be difficult to get 24 volts out of the thermostat unless you have a common wire (C) on the thermostat. Most 4 wire thermostats only have one hot wire and no common so you can not test 24 volts unless you have a common on the thermostat. You might have a short in one of the thermostat wires causing this problem. Best of luck in finding the problem. Steve

  28. I have a concord heat pump that the outside unit will not come on. I opened the panel up to see the contactor, is not being pulled in, but has a control board next to it with a flashing red and flashing green light. I don’t have the book for it and have not found any info yet on line. Any idea what and why both lights are flashing?

    1. Hi Chris! I am sorry, but I do not have any information on Concord heat pumps. I would suggest tracing the 24 volts down starting at the furnace or air handler control board. You should have 24 volts AC between Y and C (com) when the thermostat is calling for air conditioning. If you are getting 24 to 28 volts AC there, then move out to the out door unit and see if you are getting 24 volts between the yellow and Common wire outside. Where the 24 volts stops is where the problem is. Best of luck in finding and fixing the problem. Steve

  29. My problem is that I am getting 27 VAC at contactor coils (Y & C) when I shut down the power coming into contactor (240VAC) and contactor works as expected. With 240 VAC coming in, coil (Y & C) voltage drops to around 15 VAC which makes open contacts. If I push the contactor manually, air compressor and fan both work fine. I found the capacitor went bad, replaced it and I also ordered a new contactor which should be arrived soon but I still think my contactor is still good (coil resistance value close to 16 ohms).
    So far I changed capacitor and filter.
    Is there anything I could check? Any suggestion will be appreciated!

    1. I am sorry I really do not understand for sure what you are trying to explain other than the contactor is not working some of the time. The coil voltage on the contactor should be between 24 to 28 volts AC and you should get 24 to 28 volts AC between terminals Y and C when the thermostat calls for cooling. 24 to 28 volts AC should be at the contactor coil when the thermostat is calling for cooling. If you are not getting a constant 24 to 28 volts to the contactor then there is a problem with the thermostat or thermostat wiring. You could have a loose or broken thermostat wire or a bad relay in your thermostat. A thermostat with low batteries (if equipped) will not produce the needed 24 volts. I checked the ohm rating on two contactors and both had a little over 18 ohms. I would think that with 16 ohms your contactor is OK. I would suggest turning off the power to the unit and disconnect the two low voltage wires that go to the contactor. Turn the power back on and set the AC to cooling with the thermostat calling for cooling. Check and see if you are getting 24 to 28 volts out of the loose wires that go to the contactor. If the voltage is OK with the wires disconnected and then drops when the wires are connected back to the contactor then you might have a bad coil in your contactor that is causing this problem and hopefully the new contactor will fix this problem. I hope you can find and fix the problem easily. Steve

      1. Yes, I meant to say that voltage drops to 15 volts at coil when input supply (240 VAC) gets connected to the contactor. Now, my ac works fine after replacing the contactor.
        Thanks.

      2. Hi! Great to hear that you fixed the problem by replacing the contactor. Thanks so much for sharing this on our site! Hope you have a great day! Steve

  30. Hello
    I have the same problem that is listed here on your site. Can the control board be done as a DIY? Where would you find the low pressure safety switch and how can you tell if it has gone off?

    1. Hi Mr. Durant! Yes, the control board can be replaced as a Diy. I would suggest taking a picture of how the old board is wired then transfer the wires to the new control board. Not all Air conditioners have high and low pressure safety switches. The low pressure safety switch would be found on the low pressure side of the compressor. This is usually the larger of the two lines. Since your contactor is not coming on I would first test the contactor coil to see if you are getting 24 to 28 volts AC when the unit is calling for cooling. If you are getting 24 volts to the contactor and the contactor does not pull down then you have a bad contactor. If you aren’t getting 24 volts to the contactor coil I would suggest staring back at the furnace or air handler control board. When the thermostat is calling for cooling you should be getting 24 to 28 volts AC between the Y (yellow) and C (com) on the control board. If you aren’t then you have a thermostat or thermostat wire problem. If you are getting the 24 volts between Y and C then continued to test with the volt meter going outside to the outdoor unit until you find where the voltage stops. Where the voltage stops then this is where your problem is located. I hope you can easily find and fix the problem. Steve

      1. Thanks for the quick response I had a new contactor and capacitor installed I will check the thermostat as indicated and the lines.

  31. Okay I am not getting 24 vots to the contactor evern thought my thermostat is set to cooler tempt than room temp. When i depress the contactor the unit turns on and AC works. I rigged the contactor switch to stay depressed just so We can have AC until repair guy comes. The only other things i can think of is a bad thermostat, or bad control board on air handler. any other thoughts ? Also is it bad that i rigged the contactor switch to stay on (I put some electircal tape and taped it closed so we could have AC.

    1. I would not recommend taping the contactor contacts shut, but if your family is hot you got to do what you’ve got to do to stay cool. Many times I see contactors that are not getting 24 volts because the low pressure safety switch has gone off. The low pressure safety switch opens the circuit most of the time because the unit is low on refrigerant charge. If this is the cause taping the contactor might cause the compressor to over-heat. Please keep a close watch on the AC to make sure the unit shuts off with the blower. If the outdoor unit runs without the blower running then the system will freeze up and possible slug the compressor out. Yes, this could be a faulty thermostat or control board. Best of luck in finding the problem. Thanks for the question. Steve Arnold

      1. I am getting 24 volts between y and c on the control board but outgoing wires from y and c to contactor do not have 24 v. What is the problem?

      2. Hi Mr. Lee!
        I would think that you have a broken wire or a safety control like a low pressure switch (your unit could be low on refrigerant) or a time delay relay, control board that is not allowing the 24 volts to get to the contactor. I would suggest testing to see where you stop getting 24 volts and this will be where the problem is. I hope you can easily find where the problem is located. Steve

Leave a Reply

Your email address will not be published. Required fields are marked *