heatpump/compressor cycle 10-15 secs on 10-20 minutes off.


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Old 07-16-18, 04:16 PM
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heatpump/compressor cycle 10-15 secs on 10-20 minutes off.

Hello, I hope someone could point me to a trouble shooting area next. We use the heat pump for the first time this summer. The heat pump had been working in cooling mode for the last few days (temperature in the 90+) fine. However since yesterday (temp still in the 90’s), the heat pump (the compressor to be exact) runs between 15-20 secs then shut off for about 10-15 minutes, runs for another 10-20 secs and shuts off again. This cycle repeats until I shut off the system. This cycling occurs even at late night where outside temp is in the 60-70. I have tested the following:

All the coils, grill, vent, filter are clean.

The heat pump/compressor does not have this problem in heat mode. Cold air is produced during the 10-20 secs that the compressor runs.

The reversing valve is controlled by a 24 v (AC) solenoid, 24v for heat, and 0v for cool. Appropriate voltage is present for the appropriate mode. I believe the solenoid is working properly.

The reversing valve seems to be working correctly, since I can hear the swooshing sound of refrigerant during switching from cooling to heat or heat to cool. I could see a magnet slide during mode switch when the magnet is placed on the outside of the valve. Although I am not 100% sure that the valve complete the transition for each mode switch.

Could low refrigerant causes this symptom? Would low refrigerant also cause the problem in heat mode?

Many thanks for any suggestion.
 
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Old 07-16-18, 08:03 PM
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Yes it sounds like you are cycling on a pressure switch.

While it is probably a low pressure switch it could be a high pressure switch.
Is the outdoor fan motor running when the compressor runs?
 
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Old 07-16-18, 08:29 PM
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Yes, the outdoor fan motor runs whenever the compressor runs. Why does the compressor have no problem during heat mode?

Where are the low and high pressure switches that I can just short the leads to test the idea?

Thanks again!
 
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Old 07-16-18, 09:09 PM
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Have you tried the heat today? I have gotten that question hundreds of times. The pressures can be very different from heat or cool mode. I have also gotten “ You installed that unit 19 years ago, if it requires replacement today it is your fault” and “ I have a maintenance agreement, I should never require parts”

It sounds like you have a refrigerant leak. You can bypass the low pressure switch but that is kinda like removing the motor oil from your car and trying to run it. The refrigerant is moving oil through the compressor. I would advise against it.

If the leak is on the low pressure side of the system you can pull air or water into the refrigerant circuit by bypassing a low pressure switch.
 
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Old 07-16-18, 09:42 PM
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Yes, I put it in the heat mode again today, and it work fine for 15-20 minutes, most likely longer, but that's all I could stand in this hot weather. I actually did this several time to be sure the reversing valve switched mode completely.

I don't mean to by pass low pressure switch to use the machine. I just need to know and have confidence of what is wrong before calling the service guy, or just replace the whole thing.

Thanks again.
 
 

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