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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?

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 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. System 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. If you have any other questions please feel free to email us at: support@arnoldservice.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 earn your business! Steve & Barbara Arnold

14 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 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

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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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