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Problem: My outdoor air conditioning unit’s high pressure switch trips ever so often. Why does the high pressure switch trip so often?

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Problem: My outdoor air conditioning unit’s high-pressure switch trips ever so often. Why does the high-pressure switch trip so often?

Answer: The high-pressure switch tripping on an air conditioner or heat pump unit can be caused by several things:
1. Dirty outdoor coil. Turn off the power and clean with a garden hose.
2. Slow or dragging fan motor. Replace motor or capacitor.  I would recommend testing the capacitor first. I would need to know the capacitor specs (uf/mfd and voltage rating) to recommend a replacement.
3. Motor or fan blade going the wrong direction. Air should come out of the top of your unit.
4. The system is overcharged with refrigerant. Would need gauges to check this.
5. Faulty high-pressure switch tripping without having high pressure. High-pressure switches are usually set to trip at a little over 300 psi. Sometimes I have seen switches trip for no reason at all.

6. A blockage in the refrigeration cycle. This could be a TXV valve or metering device that is partially stopped up or not working correctly.

7. Extreme high outdoor temperatures above 100 degrees. Your outdoor unit has to be clean to run properly under high outdoor temperatures. I would recommend that your unit is thoroughly cleaned and charged properly. If you have any other questions please feel free to email us at arnoldservice@gmail.com or comment in the comments section below. We would love to answer your questions and have your business!

We hope you can easily find and fix the problem. We would love to help you out and try to earn your business! Steve & Barbara Arnold

52 thoughts on “Problem: My outdoor air conditioning unit’s high pressure switch trips ever so often. Why does the high pressure switch trip so often?

  1. I have a 2015 Frigidaire Package unit and try as we might we can hit the sweet spot with the freon where the unit will work routinely for both heating and cooling. It seems like their microchannel design is flawed. I heard that many companies have moved away from this design in the air handler for this reason. Do you know what options we may have?

    1. Hi Shawn! I am sorry, I am not a Frigidaire dealer or distributor and have never installed Frigidaire equipment so I have not heard of any problems with the Frigidaire HVAC systems. Sorry, but I have not heard of Frigidaire’s microchannel design. I know that many of the manufacturers have had recalls on TXV valve problems because Copeland did not install the right rust inhibitor in the compressor oil and this caused thousands of TXV problems. Some manufacturers paid for TXV valve replacements and refrigerant flushing solutions to clean up the problem. I am guessing that you might have a TXV problem. I am very sorry that I can not give you any advice and can not be of any help. Maybe someone else will see your post and have a solution. I would like to suggest trying to contact Frigidaire about the problem and see what they say. So sorry to hear you are having this problem! Steve

  2. Hi Steve,

    Thank you for all the great info here.

    I have a heat pump – it runs for a while (2-3 hours) then the compressor would stop working (short cycling code will come on) – the contactor would be pulling but compressor won’t run. I have changed the air filter, cleaned inside coil and outside coil, new contactor, new capacitor, new thermostat and had a technician check the refrigerant level (all good). Technicians can’t figure out what’s going on. Any guidance would greatly be appreciated. Tnx

    1. Hi! The question would be what is causing the compressor to stop working in the middle of a cycle. I would suggest that you or someone check to see if the compressor is overheating and going off on thermal over-load or if the heat sensor that some compressors have on the top of some of the scroll compressors is opening up because of the compressor overheating. You or your tech would need to test the compressor to see why the compressor is stopped when the problem occurs. This could be hard to get your service tech there when your unit is acting up since the problem is erratic. You or the service tech would need to check to see if the compressor windings are open? Is there power going to the compressor windings when it stops or is something shorting out that is cutting off the power to the compress? There have been lots of problems with TXV valves failing. If your TXV is not working correctly it can cause the compressor to overwork, overheat, and go off on thermal overload. If your tech has not already made sure the refrigerant charge is right if you have a 410A unit make sure the subcooling is right. I hope that you can easily and inexpensively find and fix the problem. Happy New Year! Steve

  3. Greetings, I have rheem heat pump unit that heats and cools with air handler inside the house. Lately the unit throws a High Pressure Lockout code on the circuit board (47-102685-06). But it does not throw any codes when it’s running on cool and it cools well.

    When I clear the code by turning the breakers off to the unit, and put it on heat, the unit comes on and then shuts off for a total of about 3 or 4 times within a 10 minute window. After the 3 or 4 time it finally throws a High Pressure Lockout again. When it is cycling (short cycling?) on heat, it flashes both LED’s for about a few minutes and then it starts up again and then shuts off again, during this time it sounds like hissing from the unit and the motor/fan sounds like it’s have a bearing go bad. It also sounds super loud when the heat kicks in, like someone slamming a door.

    None of this happens when I reset the unit by turning off the breaker and putting it on Cool, everything works fine, no hissing noise what’s so ever.

    Could it be high pressure switch sensor? Capacitor? Motor Fan? Reverse Valve? The outside unit is completely clean except for one side that’s got a bit of dust build up as in it’s not super dark brown but just 10 to 18 % of dust covering up on that one side.

    1. Hi Fred! This sounds like you might have a slow blower motor or your indoor coil is dirty. I would like to suggest that you make sure that the capacitor on your indoor blower motor is in good condition and your indoor coil is good and clean. On heat pumps the indoor coil becomes the condenser in the wintertime and if you are not getting enough airflow across the indoor coil it with cause the high-pressure code problem. A restriction in your refrigeration cycle like a bad TXV (thermostatic expansion valve) or a stopped up orifice can also cause high-pressure problems. I would try checking the capacitor and clean the coil first since they are the least expensive fixes. If that does not work you might need to install gauges and see what the pressures are running in the heating mode. I hope you can find an easy and inexpensive fix. Steve

      1. Steve,
        Hi, thank you very much this forum there is a lot of useful info on here.
        I too am having an issue with my 2012 5 ton York Air Conditioner unit.
        Here’s the scenario. In August 2019 I noticed a loud sound coming from the upstairs outside air condenser. It sounded like a generator sound that would last for 45 seconds before shutting off. I would shut down the unit from my phone and restart after delay and it would work fine. This was about the last time I would use the unit for the season.
        Starting in May 2020, we used the units again. We noticed that the unit would run but it didn’t feel so cold. I brought in a local contractor who said the unit was undercharged and we needed to change the capacitor, that work done.
        Soon thereafter, we would still hear the noise. The outside condenser would make a loud chattering sound and the compressor would shut off. The condenser fan would still run. If we didn’t notice the sound- the inside thermostat would continue to run and the air would not be cold. I would then shut off the unit and wait for delay, restart unit and it would be fine, until the same situation occurs.
        The unit blows cold air until the sound comes and compressor shuts.
        This happens on occasion. I would run outside and hear the liquid line banging against the condenser which is the sound i would hear…the liquid lines would be moving pretty hard and fast and then the compressor would shut off.
        The next few months I struggled with this and brought in guys who all said I was low on refrigerant and changed compressor, contactor, txv valve…all with the same result.
        The last contractor said my compressor is shot and I need a new condenser. My warranty company provided a Goodman when I wanted a York. I was not home when they started and had them stop. They capped the York unit and its now sitting on the slab.
        My question is…what is causing the liquid lines to vibrate so fast and hard to cause that knocking against the condenser?
        All HVAC guys said I was low on refrigerant and the last guy said my refrigerant was fine…should I have someone hook up the York unit and put refrigerant and check for a pressure issue or should I just get a new condenser? If I get a new condenser what if their is a leak in the liquid lines? That wouldn’t solve my problem.
        Any advice would be greatly appreciated. Thanks in advance

      2. Hi Eric! I have never heard of an air conditioner’s liquid lines start vibrating so much that makes a loud noise. This sounds like you have a restriction in your system. I would like to suggest that you or you have someone try to install gauges and see what the pressures are doing when the noise occurs. I have heard units make some really loud noises when they go off on what is called “high head”. High head pressure can be caused by a dirty condensing unit, a slow condenser fan motor or a motor that stops, and over-charge of refrigerant or a restriction in the refrigeration cycle. You said that they replace the TXV because a bad TXV could cause the problem also. I have been told that compressors that have the internal mounting springs broken can make terrible noises too. So you might need a new compressor. The pressure readings when the problem occurs should tell the story of what is happening. I will leave that up to you as to whether you want to reinstall the York unit or install the Goodman unit. Goodman does have a good at least a 5-year warranty on parts. Some of the units carry a 10-year warranty. It is the labor that can be costly. Your York unit should last more than 8 years, but if it has been running low on charge or had restriction issues then I would probably recommend a new unit. Running low on refrigerant and other problems can most certainly shorten the life of a unit. You should also get a matching indoor coil to match the new unit if you do decide to get a new unit. I do not like Goodman very well. I like Trane and American Standard the best. Sorry that I can not be of much help. Steve

  4. Hi Steve,
    We have a Lennox residential AC split system, about 6 years old.
    Our outside A/C unit is running intermittently. Here is the sad, confusing, frustrating story…

    We heard a buzzing noise coming from our attic unit, called some A/C folks, they sent their tech out and he said we were low on refrigerant by about 25%. He filled it to the factory specifications and the buzzing noise from the attic unit stopped. We figured it was the coils freezing up and the fan running hard. The tech did not see any other signs that would be making the buzzing sound (no dirty coils in the attic unit, the fan was not off kilter, the bearings were fine, the filter is newly replaced, etc). We have not heard any buzzing from the attic. Though…

    A day or so later, when then hear a buzzing sound, but now coming from the outside unit. At that point, the outside fan was still operational and cold air was still coming from the inside ducts/vents , but still it was an unsettling sound nonetheless. After a while now the fan in the outside unit only partially works.

    How our day has typically unfolded in the past few days: the outside unit cools/runs fine in the morning hours, until about 3/4pm (it does not matter if it is 70s outside or 90s), then does not run (the thermostat kicks on and the attic unit blows air but the outside fan does not come on), but then the outside unit is operational again about 4 hours later in the evening.

    We got the same tech (of course when he shows up the outside unit is running fine…) and he replaced the contactor (it looked somewhat burnt, he thought due to arching). The tech said that the refrigerant levels/pressures are fine, the voltage/power levels coming into the unit are fine as well, the wires looked fine, the capacitor looks good. Essentially, he could not think of anything else that would cause the fan to not blow/outside unit to work. However the problem persists…the outside fan stopped at about 5pm but was then operational at 9pm, after about 4 hours of running it.

    So I guess my question is could it be a faulty high/low pressure switch or some thermal overload switch? And do those switches shut off for about 3/ 4 hours as a safety precaution (and can explain our lost 3/4 hours each day?) And if it is the case, would that be just another symptom of some larger cause? From my Googling, I know a dirty condenser, non-condensibles in the system or refrigerant overcharge are likely suspects, but given what the tech has told us, I could only think non-condensibles would be feasible since he said the condenser looked fine and just filled up the system to refrigerant specs. Is there a way to test for those in the system?

    Any advice/help would be very appreciative 🙂

    Best,
    Mike

    1. Hi Mike! Sorry that you are having these problems with your AC unit. It sounds like the main problem is that the fan is cutting off. If the fan is cutting off and the compressor is running then I would think that you have a fan motor problem and you probably need a new fan motor to solve the problem. If the whole unit with both the compressor and fan shuts off then I would suggest taking a look at the contactor when the unit shuts off. The question would be…”Are the contacts pulled in on the contactor”? If the contactor is loosing 24 volts to the contactor coil and the contacts are open and not pulled in then I would think that you have a low voltage problem that could be caused by the thermostat (make sure batteries on the thermostat are good) make sure thermostat is sending 24 volts between the “Y” and “C” “COM” wires, make sure that the high or low-pressure switches are not opening up an causing the low voltage to stop. If the contactor on your unit has the contacts pulled in and both the compresssor and fan are not running then I would think that your compressor and fan are going off on thermal (over-heating) over-load which could be caused by a weak capacitor, low high voltage (make sure you have at least 220 volts high voltage) a restriction in your system (bad TXV valve, stopped up restrictor orifice, or unit has water in the system causing a restriction in your system when the water in the system freezes up over time). If you have a restriction this would be found by attaching manifold gauges and watching the pressures in your system. I hope you can easily find and fix the problem. Steve

      1. I have a very similar problem on my outside Lennox AC unit. I replaced the contactor, had the capacitor checked and it was good but still my unit will run fine for a couple of days and next thing I know the inside unit is blowing warm air and outside unit is not on. I jumped the thermostat to see if my thermostat was the problem and that didn’t trigger the outside unit to come on. I happened to reset the HP switch and the unit will run again for couple of days and turn off. Each time I find that the HP switch has tripped but not tripped outside or inside breaker. I’ve washed the coils, changed the 3amp fuse in my furnace but the problem persists. Is it time to have the HP switch replaced?

      2. Hi Leticia! Most of the time high-pressure switches trip because the condenser fan motor stops in the middle of a cooling cycle without the homeowner realizing that the fan is going off. Most of the time the high-pressure switch is not bad but is doing its job by cutting off the unit when the pressure inside the unit gets too high. I would suggest that you use an Amprobe if you have one and see what the amperage is that the motor is running. The amperage should not be over the FLA (full load amp) or RLA (running load amps) for the motor. If you do not have an Amprobe then you could turn the power off to the unit after your unit has run for an hour or so and see if the condenser fan motor is getting hot. Too hot to touch means that you probably need a new motor. Another cause could be a bad TXV valve where the TXV valve is not opening enough and causing a restriction in your system. This would create high head pressure in your system. You would need to determine this by attaching manifold gauges to your unit. There have been many recalls on the TXV valves lately. There is a really good YouTube video on the following page: https://www.youtube.com/watch?reload=9&v=Amo2eRlYrzg If you do not want to watch the entire video then you can skip to the 6:30 mark where the service tech explains why so many of the TXV valves are going bad. I would like to suggest that you see if your fan might possibly be shutting off on you in the middle of a cycle or see if you have a restriction in your system by checking with gauges. I hope you find an easy inexpensive solution to the problem. Steve

  5. My question is about a 4 year old 3.5 ton fixed orifice Nordyne micro-channel AC only system. Is it common for these micro channel units to take a while to become stable and be touchy about charging rate ? These units require you weigh in the exact charge amount. I think these tiny coils restrict faster and you have to go slow with the charge like 1/4 pound then wait 20 min. I had a Tech over to discover a small leak which would loose charge after 30 days. Tech said micro-channels are know for that and not a fan of the new technology. Fan speed ok, coils clean,filter non restrictive,ducts, no damage. He could not detect the leak using sniffer or see any obvious oil leakage but surmised based on experience of know problems.

    1. Hi Don! I am sorry, but I am not familiar and do not know anything about micro-channel Nordyne units and how they can be charged. I hope that someone will see your post and have some knowledge about this Nordyne AC unit. Thanks so much for asking the question. So sorry, again that I can not give you an answer. Steve

  6. Hi Mr Steve,

    Our AC was not working for 3 days so our neighbor which is an electrician tried to fix it. He said that the unit is not turning because of a faulty High power switch, he said the wire goes through the HPS and does not provide signal to the motor to turn on. So he by passed the HPS and connected the wire somewhere else so it will send power and the AC unit turned on. Its working right now but my question is this a good idea? Can the AC continue to run w/out HPS being fixed? He said he can fix and replace the HPS but will be a lot of work and costly? Should we leave the Ac as it is whithout a functional hps? Please your advice is needed.

    1. Hi! Thanks for asking this question. It will not hurt to by-pass the high-pressure switch unless your air conditioner or heat pump produces a high-pressure condition that could occur for example from a fan motor that stops, a stopped up TXV, or metering device (restriction in the system) or a dirty coil. If you are not at home and the air conditioner continues to run under high pressure this could damage the compressor and you would either need a new compressor or a new unit. Yes, your contractor is right by telling you that the high-pressure switch is expensive to replace because most replacements require opening up the system, reclaiming the charge brazing in a new high-pressure switch, installing a filter drier, evacuating the system with a vacuum pump and recharging the system. This is about a 3 to 4-hour job and can be pretty expensive. If the unit is fairly new under 10 years old I would probably have the high-pressure switch replaced. If the unit is over 10 years old I would watch the unit closely to make sure that it is not running high pressure a let it run. That is your decision. With almost all air conditioners if you are home to hear and turn the unit off when running high pressure that is great and you have saved your unit, but if you are not at home to hear the problem for days then it could ruin your AC unit. The compressor is protected by a thermal over-load switch and when running high pressure this switch will open the circuit and stop the compressor. If you let this over-heating condition high-pressure condition continue over several days then this could cause the compressor’s thermal switch to wear out (not reset) and ruin the compressor. Steve

      1. Thanks so much for this useful info. I have same question, different context. I am a renter in a building that just replaced one of our through the wall ac units last year. The unit gets a lot of use in the summer, e.g. on all night. This year, the condenser stopped working, and a maintenance guy came and bypassed the high pressure switch – just clipped and stripped two wires and joined them with a screw on cap – he said it the HP switch wasn’t really necessary. Now, it’s their building, their unit; they vacuum coils and replace filters annually, and we have a working circuit breaker in the apartment (and renters’ insurance). I’m glad to have the unit cooling the main room again, but wanted to check – is this a risky fix for, say, a sleeping family in a small apartment?? Or if we leave it on and go out (I take a family member to medical appointments and we might leave ac on low for a few hours on a hot afternoon). Any advice?

      2. Hi! Thanks for asking this question. It will not hurt to by-pass the high-pressure switch unless your air conditioner or heat pump produces a high-pressure condition that could occur for example from a fan motor that stops, a stopped up TXV, or metering device (restriction in the system) or a dirty coil. If you are not at home and the air conditioner continues to run under high pressure this could damage the compressor and you would either need a new compressor or a new unit. Yes, your contractor is right by telling you that the high-pressure switch is expensive to replace because most replacements require opening up the system, reclaiming the charge brazing in a new high-pressure switch, installing a filter drier, evacuating the system with a vacuum pump and recharging the system. This is about a 3 to 4-hour job and can be pretty expensive. If the unit is fairly new under 10 years old I would probably have the high-pressure switch replaced. If the unit is over 10 years old I would watch the unit closely to make sure that it is not running high pressure a let it run. That is your decision. With almost all air conditioners if you are home to hear and turn the unit off when running high pressure that is great and you have saved your unit, but if you are not at home to hear the problem for days then it could ruin your AC unit. The compressor is protected by a thermal over-load switch and when running high pressure this switch will open the circuit and stop the compressor. If you let this over-heating condition high-pressure condition continue over several days then this could cause the compressor’s thermal switch to wear out (not reset) and ruin the compressor. Steve

  7. Great web page here. Lots of helpful info. I know in previous posts you say that bad high pressure and low pressure switches are rare. I have 24v coming from thermostat when calling for cooling, but contactor never gets it. I checked continuity on the LPS and it’s good. I tested continuity on the HPS and it is open. With all power to the system off, would this not be indicative of a bad high pressure switch? I would think pressure would equalize once the system is fully powered off, and not have a side be high. Finally, on a Goodman GSC13 from 2011, would the HPS be serviceable without evacuating the system?

    1. Hi Brian! Thanks so much for your kind words. Since your high-pressure switch is open then this could be caused by a bad high-pressure switch, an outdoor fan that does not work, a dirty condensing unit, or a restriction in your refrigerant system. If you have a bad restriction in your system then the pressures might not equalize. You would need to attach manifold gauges to see if you have a restriction, an actual high-pressure problem, or what the problem is. I am not familiar with the Goodman GSC13 unit that you have. I have not done any service work since 2005 so I do not know if the high-pressure switch is replaceable without reclaiming the charge or not. Most all that I have seen back in 2005 were not replaceable without brazing the new switch in place. I would suggest hooking up some gauges to see what the problem actually is. Sorry that I can not be much help. Steve

  8. The control board on my ac/heat pump shows a high pressure switch fault. I had a problem with the unit blowing the 3 amp fuse when switching to heat. I replaced the fuse and cleaned all the coils and it appeared to be running fine in ac mode and heat mode. But that is when I discovered the 02 fault which the book says it is the high presure switch. Do I need to replace the switch even though the unit appears to be running ok. The unit is 3 years old and is a nordyne unit.

    1. Hi David! I am sorry, I am not familiar with high-pressure switch operation on the newer heat pumps. Hopefully, since you cleaned your unit the pressure switch fault will not occur again. If the high-pressure switch continues to flash the high-pressure switch fault code then I would like to suggest that you or a service tech install gauges to see if the pressure is actually high or if the pressure switch is bad. On the older pressure switches, they were brazed into the refrigeration lines and they are impossible to replace without reclaiming the refrigerate charge, brazing in a new high-pressure switch and liquid line filter drier, evacuating the system to get any air or moisture out then recharging the system. This can be very costly and labor-intensive. I would recommend that you have your heat pump checked out to make sure that you really are not running high pressure so it does not ruin your compressor. If it is a high-pressure switch that is bad then I would suggest replacing it only if you do not have to break open the refrigeration system. Anytime air, moisture or dirt can be introduced into the system then this is not good. If the pressure switch is an easy replacement then I would do the replacement only if the high-pressure switch is actually bad. Most of the time high-pressure switches do not go bad very often. I hope you can find out if you really have a pressure switch problem or not soon. You make want to turn the power off to your unit for 30 seconds or so and see if the flashing code resets and goes away. I hope that it will go away. Steve

  9. Hi Steve
    I looed at a heat pump today and found it shutting down on the high pressure switch. It is a new installation and appears there is not enough cfm passing through this 3 ton unit ( by my calculations only about 900cfm) – Would or could that cause the high pressure situation? Never seen this before – it is in the heating mode. thank you in advance for any help you can give – Dennis

    1. Hi Dennis! If you are in cooling mode with the new outdoor unit is going off on the high-pressure safety switch then I would think that your unit is over-charged or you have a restriction in the refrigeration cycle. About the only way that I can suggest to tell what is going on with the unit would be to install gauges and see what the pressure readings are. Is the pressure actually high or is there a problem with high-pressure safety switch or defrost control board. Hooking up gauges would tell you if the TXV (thermostatic expansion valve) is causing the problem. 900 cfm would not be enough if you are talking about the indoor unit having only 900 with the unit in the heating mode because as you know it should be 440 cfm per ton and 900 would not be enough for a 3-ton unit. I hope that you can hook up some gauges, find and fix the problem. Steve

  10. an a/c guy disconnected the high pressure switch on our outdoors 2002 Ruud unit because it kept tripping and he said the switch was not needed. yesterday we had a bad storm go through and the electricity went out several times. then after storm passed unit would not cool. I went outside and the top of the fan blade area was extremely hot and blades were not moving. what happened? did not having the pressure switch have anything to do with it? he came out again last night and says that the compressor etc needs replacing and it is going to cost another $900.00 after last years $795.00 he charged to work on it and when he disconnected the high pressure switch

    1. Hi Danna! So sorry to hear that this happened to you! If your unit was kicking off the high-pressure switch this is a good sign that either the high-pressure switch is bad (which is unusual) or your unit is dirty, over-charged, has an obstruction if the refrigeration system or has a slow fan motor. Since the fan motor went out after the storm this is a sign that more than likely the fan motor was going bad, moving slow and was causing the high-pressure switch to go off. If the service tech installed gauges to test your system then he should have seen the high-pressure problem. The service tech was probably trying to prevent you from having trouble with your AC not working, by disconnecting the high-pressure switch. This is not advised because this protects from hurting the unit. The unit should not have been running in a storm. I always recommend turning AC units off during storms because this can be fatal with power going off and on, power surges and lots of water. I will let you decide who is at fault. I do not like to take sides in these kinds of situations. So sorry that you are out of AC! Steve

  11. My outside heatpump at time will drop out the compressor, even though the compressor contactor is pulled in and a volt measuring indicates 240 on compressor side of contactor
    The compressor was recently replaced as were the caps. When running the compressor is drawing a around we amps the start wire has 6amp on it.
    So I’m wondering why the compressor stops running. When it is running make very good heat or cooling.
    It some times runs several days without any symptoms.
    I’m starting to wonder if the reversing valve is getting erratic. What do you think?

    1. Hi Loren! My best guess would be that the compressor is over-heating and going off on thermal overload. I would like to suggest that you turn off the power to the unit and touch the top of the compressor to see if it is hot the next time the compressor cuts off unexpectantly. If the compressor is hot then this could be caused by a dirty condenser coil, a fan motor that is cutting out or running slow, (not up to speed) running low on refrigerant, a restriction in the refrigeration cycle or a faulty TXV valve. Many of these problems can be determined by installing gauges and looking at the pressures to see what is wrong. I would also recommend turning off the power to your unit and check all wiring to make sure everything is good and tight. I would highly recommend taking the compressor terminal cover off and inspect the 3 wires that go into the compressor. Make sure they are tight and there is no burning in those wires. I hope you can easily find and fix the problem. Other than those things I have no idea. Steve

  12. Hi, I recently purchased a new house with a carrier ac unit. this is our first summer and the ac is not working. The psi level is at 700 which is extremely high for a 3.5 ton unit. Do you have any recommendations on what the problem could be? the unit runs for 30 mins then it stops blowing cold air.

    1. Yes, this is extremely high and should not happen. This sounds like you have a stoppage in the refrigeration system somewhere. There have been lots of problems with TXV valves so this could be the problem or you might have a fan motor that is running too slow. If the fan motor is running slow then I would recommend checking to make sure that the fan motor capacitor is in good condition and up to specs. I would recommend that you have a tech install gauges and find and fix your problem. 700 psi is very dangerous and could cause leaks in your system. Steve

  13. hello steve
    I got a System with 134a that will run for about 2 seconds and then trip on high pressure. I gauged it up and it trips at 400 psi. Any ideas on issue?

    1. Hi Carlos! This sure sounds like you have a restriction in the system. I know that several manufacturers have been having problems with TXV valves getting stopped up, but I do not know for sure. Here is a link to a good video on how to determine a bad TXV: https://www.youtube.com/watch?reload=9&v=L7VkLsXGaQ8 The AC Service Tech Youtube Channel has many videos that should be able to help you out. I am sorry, but sometimes it is hard to find out where the restriction is located. I hope you can easily find and fix the problem. Steve

      1. Thank you steve,
        My other thought was the compressor since this unit has been running for a years with no issues till no. I just found it weird that it will trip so quick on high pressure.

      2. Hi Carlos! Yes, that is weird that it trips so quickly on high pressure. I had a Copeland scroll compressor that did this and it turned out to be a stuck check valve that was in the high-pressure discharge line of the compressor. It was located right outside the compressor’s discharge line. I could not believe that happened and I had to replace that valve to fix the compressor. I hope that is not your problem and it is something that is an easy fix. So sorry for your trouble. I know it can be a pain trying to figure out what is wrong. God bless you. Steve

  14. Hi Steve,
    I am working in an industry on a HVAC system. The outdoor temperature is around 46 degree Celsius right now.
    And we need the HVAC to be working at any cost but the problem is that the compressor often trips with high pressure alarm. Is there any specific reason to that?

    1. Hi Abhishek! Here are the reasons that I list in this post. The following are the only reasons that I can think of that would cause a high-pressure alarm to sound:
      1. A dirty outdoor coil. Turn off the power and clean with a garden hose. 2. Slow or dragging fan motor. Replace motor or capacitor.  I would recommend testing the capacitor first. I would need to know the capacitor specs (uf/mfd and voltage rating) to recommend a replacement. 3. Motor or fan blade going the wrong direction. Air should come out of the top of your unit. 4. The system is over-charged with refrigerant. Would need gauges to check this. 5. Faulty high-pressure switch tripping without having high pressure. High-pressure switches are usually set to trip at a little over 300 psi. Sometimes I have seen switches trip for no reason at all. 6. A blockage in the refrigeration cycle. This could be a TXV valve or metering device that is partially stopped up or not working correctly.7. Extreme high outdoor temperatures above 100 degrees. Your outdoor unit has to be clean to run properly under high outdoor temperatures. I would recommend that your unit is thoroughly cleaned and charged properly. I hope you can easily find the problem and get it fixed soon. Steve

  15. Hi Mr. Arnold – I have an old Tempstar 5500, Model CH5524VKA2 installed 1993. It’s our 25th Anniversary! The low pressure sensor on it is stuck open so the heat pump won’t start. It looks like the sensor can be easily replaced by unscrewing a nut but I’m worried that the refrigerant will escape. Would you know if there’s a schrader valve in there so I can do it myself? While I’m there, I’m thinking to replace the coil’s temperature sensor which looks pretty easy. But there’s this dense, black material around it and I’m wondering if that’s for insulation or just to keep the sensor in place? Thank you!

    1. Hi Gary! So sorry for the delay in answering your questions. We have been swamped with orders today and I did not get a chance to answer. I have never seen a low-pressure sensor from the factory that has a Shrader valve. Most of the time to replace the valve a new one has to be brazed into place. If it was me I would bypass the valve by joining the two wires together that go into the valve so you can use your heat pump. I would not recommend opening up a 25-year-old heat pump to replace a defective low-pressure sensor valve. I would recommend bypassing the sensor and keep a watch to make sure the heat pump does not run low on refrigerant charge. Most of the time the coil’s temperature sensors are held in place by a metal clip and the black gum insulation tape is used as an insulator. Thanks for asking the questions. I hope you have a great day and week! Steve

  16. I can push the contactor in and the fan comes on, but when I release it stops. I replaced contactor and capacitor too

    1. Hi Tommy!
      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

  17. Steve,

    I’ve narrowed down my problem to a bad high pressure switch. Is there a way to replace the switch without draining the system?

    Shawn

    1. Hi Shawn! The only way I know to replace a high pressure switch is by brazing a new one into the refrigeration circuit. I would suggest that you by-pass the switch by joining the two wires together. I would suggest that you install gauges to make sure that the pressure is not actually running high. Problems that would cause high head pressure would be a dirty condensing unit, slow fan motor, over-charge or refrigerant or a blockage in the refrigeration cycle. Most of the times high pressure switches are doing their job by protecting the unit from harm and rarely go out. Steve

  18. Just replaced the motor and capacitor. Fan won’t move, when the unit is turned on it just says “trip”. Not sure what to do next.

    1. Hi Shannon! So sorry to hear that you are having problems with you outdoor AC unit. If the high pressure safety switch is tripped it will not allow the fan to start because the safety switch will not allow 24 volts to go to the contactor to get the compressor and fan motor started. I would suggest that you try to reset the tripped switch, usually by pushing it in with your finger. If the high pressure switch will not reset then you either have a bad high pressure switch or you have a blockage in your refrigeration system that is causing high pressure in your system. I would suggest that connect some gauges to your unit to see what the pressure is actually doing in your system. You should be able to temporarily wire around the pressure switch by turning the power off to the unit and joining the two wires together that go into the high pressure switch. I hope that when you say, “trip” that you are referring to the high pressure switch and not the circuit breaker. If you have more questions please let me know by emailing me at arnoldservice@gmail.com email address. I hope you can easily find and fix the problem. Steve

  19. Steve, thank you so much for all of your help and guidance. I couldn’t have narrowed this down without you. I was searching for the wires that were coming from the thermostat to the condenser and uncovered a HUGE problem. Had the inspector seen it before we bought the house, we wouldn’t have made the purchase (with a list of other issues to add). Previous owner/s had covered up the rusted, chewed up, taped up in multiple places, green and burnt colored, muddy and wet thermostat wires. Basically mucked them up real good and then put about 7 band-aids on them within about a 18″ span. Pulled them, reran new, hooked it all back up and wallah! Perfect! Thank you again, Steve !

    1. Fantastic! Glad to hear that you found and fixed the problem with little expense! I appreciate your kind words and letting us know what the problem was! God bless you and your family today and always! Steve

  20. Steve, we narrowed it down to the culprit! The wires that are coming from the thermostat to the contact, were chewed to all get out. I pulled back the blue flex-hose that was protecting the thermostat wires from the condenser to the house, and found the wires and been chewed up by what appeared to look like a weed-eater. Wires were rusted, taped in about 7 different places, muddy and wet, green colored exposed wires etc. just NASTY looking and came apart with one gentle tug to get it out of the house wall a little bit. Surprised they hadn’t shorted out or burned anything up, or down. Bought new wire and air return filter for $15, ran it, connected it all up, and WALLAH! Thank you Steve for all you do and for all of the help!!

    1. Fantastic! Glad to hear that you found and fixed the problem with little expense! I appreciate your kind words and letting us know what the problem was! God bless you and your family today and always! Steve

  21. my condenser unit isn’t running. The inside unit is blowing air. I check outside at the contactor and it is in the disengaged position (closed circuit). I can manually turn the unit on if the bridge/switch is held down, but it shuts off as soon as i let up. I have 220 voltage on one side coming in, but none coming out unless I hold that bridge down. Could this be a high or low pressure sending unit and can I as a home owner do it myself? I dont make much money so I try to pinch everywhere I can. If I have to call someone out I can, but I try not to. Thank you for your reply and help!

    1. Hi Jerry! I would suggest checking to see if you are getting 24 to 28 volts AC to your contactor coil. If you are not getting the 24 volts to the coil then we cover 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/ If you are getting 24 volts to the contactor coil and it isn’t engaging then you have a contactor problem and you need a new contactor. We sell many different contactors on the following page: https://arnoldservice.com/product-category/air-conditioner-parts/ac-contactors-heat-pump-contactors/ Yes, this could very well be a low pressure (low refrigerant) switch that is cutting the unit off for protection. I hope you can easily find and fix the problem. Steve

      1. Thank you Steve! Now…how to check that darn 24V. lol. I know (i suppose) I have 248 coming in from the power source(condensers own small breaker box which is mounted to the house directly beside the condenser) to the conductor switch, but Im not sure which of the remaining 6 prongs to check for the other side of the contactor 🙁 2 prongs seperate the bridge, or the place where contact opens the circuit. The other 4 remaining prongs are at the oposite end of the 220 side. I wish I could upload a picture of what Im looking at for you guys. I’m so ignorant with HVACs. I know its 248 “coming in” because there are three wires, white, black, and a gnd. I turn my multi-meter to ac, A~, and V and the leads on the white and common/black wire and it spits out 248+-. I move to the top of the contactor and I have 4 wires with 4 prongs, all but right up against each other. Thank you again so much for your help, Steve!

      2. Hi Jerry. Please see the video that we have 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/ It shows how to test the contactor coil to make sure it is getting voltage. I hope you can get the problem fixed soon. Steve

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