Heat pump shutting off

**Dan Harris** · 10-23-2009, 05:55 PM

Todays inspection the heat pump, on the cooling cycle ran for 30 seconds, then shut off for a few seconds, ran, shut off, after it did this for a few times I shut the unit down. For the time that it ran it was cooling.
What would cause this?
I ran the heating cycle first, It didn't do it on the heating cycle, and I don't believe it started shutting down untill the unit was running, on cool for 30 or so min.

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**John Goad** · 10-23-2009, 06:24 PM

Could be the high pressure switch, are you sure the condensing unit came on in the heating mode or could it have been the heat strips providing the heat?

**Dan Harris** · 10-23-2009, 06:34 PM

Originally Posted by John Goad

Could be the high pressure switch, are you sure the condensing unit came on in the heating mode or could it have been the heat strips providing the heat?

No. The unit didn't have heat strips.

**Bruce King** · 10-23-2009, 06:41 PM

My guess would also be a pressure switch or actual pressure problem but for the DIY, it would be easy to replace the main contactor to see if that is the culprit. These are high failure items, the 28 volt coil could be opening up or the contacts worn. Another common problem is loose connections in the disconnect or at the breaker. Also loose thermostat cable connections or even a flaky t-stat.

**Jim Luttrall** · 10-23-2009, 07:03 PM

Not enough information to even begin to know what the problem is.
What was the outdoor ambient? Indoor ambient?
My first suspicion would be a low pressure switch, especially if a operating in low temperatures. Could be high pressure if outdoor ambient was high.
Need more information, but as far as the recommendation, it needs service unless you were operating it outside or near the temp. limit.

**Dan Harris** · 10-23-2009, 07:10 PM

Originally Posted by Jim Luttrall

Not enough information to even begin to know what the problem is.
What was the outdoor ambient? Indoor ambient?
My first suspicion would be a low pressure switch, especially if a operating in low temperatures. Could be high pressure if outdoor ambient was high.
Need more information, but as far as the recommendation, it needs service unless you were operating it outside or near the temp. limit.

Out doors it was apx 70 degrees when I ran the heat.
Shut it down for apx 30 min. before switching it to cool.
About 75 in and out when I started it on cooling.

**Jim Luttrall** · 10-23-2009, 07:19 PM

I'm guessing cycling on low pressure switch. I'd be looking for clogged indoor coil/filter first, then proceed to check the refrigerant level, clogged filter dryer, defective metering device, and proceed from there. I assume you checked the filter and maybe looked at the indoor coil.
Bottom line though is it needs service UNLESS it is a clogged filter.

**Dan Harris** · 10-23-2009, 07:28 PM

Yea everything was clean.
Guess this is another good reason to go around the home a couple times.
I may not caught it otherwise.

**Jerry Shipman** · 10-26-2009, 08:17 AM

Was the entire unit shutting down? Compressor and fan, or just the fan? Could be a low ambient set up with a thermostatic control, cycling the outdoor fan off and on to keep head pressure up. It shouldn't have taken thirty minutes, but as the heat load in the house came down, the system temp, along with the return bend, or coil temp where the temp sensor was located would also drop; possibly to just below the switch setpoint. Its possible the switch was not working properly, or the unit charge was incorrect. Either way, a good service tech should take a look.