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heat pump short cycle


John Dirks Jr
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At a recent inspection I was testing the heat pump in heat mode.  On the initial startup the unit short cycled 4 or 5 times so I shut it off and waited a while.  The short cycle events lasted maybe 30 seconds each.  I tried a second time and it did it 2 more times and then stayed on like you would expect.  From then on it functioned normally during the remainder of the inspection and produced adequate heat.  

Just to be sure I wrote it up describing the condition and recommended evaluation by an HVAC tech.   

So, is this short cycling surely an indication of a potential problem or could it be part of normal functions?  

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On 4/21/2022 at 6:42 AM, John Dirks Jr said:

At a recent inspection I was testing the heat pump in heat mode.  On the initial startup the unit short cycled 4 or 5 times so I shut it off and waited a while.  The short cycle events lasted maybe 30 seconds each.  I tried a second time and it did it 2 more times and then stayed on like you would expect.  From then on it functioned normally during the remainder of the inspection and produced adequate heat.  

Just to be sure I wrote it up describing the condition and recommended evaluation by an HVAC tech.   

So, is this short cycling surely an indication of a potential problem or could it be part of normal functions?  

I've seen about 10 heat pumps ever, but don't they have a defrost cycle that it may have been going through?

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On 4/22/2022 at 1:07 PM, Jerry Simon said:

I've seen about 10 heat pumps ever, but don't they have a defrost cycle that it may have been going 

All the components, except the outdoor fan, should operate during defrost.  The reversing valve just sends hot refrigerant through the outdoor coil.

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On 4/21/2022 at 2:29 PM, Bill Kibbel said:

At the outdoor unit, did you listen for the compressor turning on and it's not just the fan running?

I would first suspect that the compressor start capacitor is failing.  Next the control circuit board.

Yes, the compressor and fan were both short cycling together

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11 hours ago, John Dirks Jr said:

Yes, the compressor and fan were both short cycling together

Sometimes, if supply registers are too close to the thermostat (on systems that rely on the temperature sensor within the thermostat, i.e. un-zoned systems), this sort of short cycling may result.

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On 4/26/2022 at 5:18 AM, Marc said:

Sometimes, if supply registers are too close to the thermostat (on systems that rely on the temperature sensor within the thermostat, i.e. un-zoned systems), this sort of short cycling may result.

Probably not the case in my situation because the demand I was calling from the thermostat was somewhere around 10 degrees above room temperature.  

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