Question: Is it OK to allow my HVAC contractor to by-pass my air conditioning unit’s high-pressure switch? We have had several contractor call-backs because our unit continues to trip our high-pressure switch. This happens routinely, each summer. The latest incident, the technician came and reset the switch after noting that all pressure levels were good, coils clean, and no apparent blockages. The unit shut down again, about 30 minutes after he left. The second technician came the following day, ran a full diagnostic of the furnace and air conditioning system, and reported that “sometimes these switches are just bad, and trip for no reason.” He by-passed the high-pressure switch- after discussion, and he was concerned that it would happen again in short order. Now, I’m wondering whether to replace the high-pressure switch or leave it by-passed? Old Lennox unit. (Pulse 21) The compressor has been replaced, the capacitor is new. I would be very interested in your opinion?
Answer: We have a post that explains why AC’s high-pressure switches trip sometime on the following page: https://arnoldservice.com/problem-my-outdoor-air-conditioning-units-high-pressure-switch-trips-ever-so-often-why-does-it-high-pressure-switch-trip-so-often/ Most of the time high-pressure switches trip because the condenser fan motor stops or is running too slow When the fan motor stops or runs slow the unit will produce high pressure and the unit will trip the high-pressure switch to protect the compressor from being damaged. This could be also caused by a restriction in your refrigeration cycle like dirt or moisture in the system. A bad TXV (thermal expansion valve) can also cause high-pressure switches to trip. Most contractors do not want to replace high-pressure switches because it is quite time-consuming and expensive for the homeowner. It is also not a good idea to open up the refrigeration system that exposes the system to air, dirt, and moisture. The worst enemies of the refrigeration system are air, dirt, and moisture. In replacing a high-pressure switch the contractor would need to reclaim the refrigerant, cut the old, bad high-pressure switch out, and braze in a new high-pressure switch in. Install a new filter drier, test for leaks, evacuate the system for at least an hour with a vacuum pump then charge the system back up with refrigerant and test the operation. Yes! this is very time-consuming. Hopefully, they installed filters driers and evacuated your system when they replaced your compressor. Any moisture in the system can freeze up after running a while then cause a restriction in the system and cause the high-pressure switch to go off. I would recommend that you keep a close eye and ear on your AC to make sure that the fan continues to run properly and you are not getting a restriction in your system. The unit will start sounding funny and will sound loud if the fan stops and if there is a restriction in your system. Your service tech needs to make sure that your AC system is not creating a high head pressure condition before bypassing the high-pressure switch. I would only recommend by-passing the high-pressure switch if your air conditioner is old over 15 years and the contractor is confident the problem is with the high-pressure switch and not some other problem in your AC system. If your unit is going off on high pressure then this will cause the compressor to overheat. The compressor is thermally protected and the thermal protection will cut the compressor off temporarily until the compressor cools down then the compressor will start again. The problem is that the thermal protection switch inside the compressor will only reset so many times. When the thermal protection switch is worn out then the compressor is bad and you would need to get a new compressor or a new air conditioning unit. I hope this helps in answering your question. Below we have a really good YouTube video on how high-pressure switches work and how to troubleshoot high-pressure switches. Thanks so very much to AC Service Tech LLC for making this video. God Bless You and Your Family Today and Always! Steve
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