On or Off?

Should a heat pump be tested if the unit as not been on for over 12 or more hours? Doesn’t the heater in the crankcase need to be on to prevent damage to the compressor?


Here where it is warm probably no problem, where you are in the cold NO it should not be tested.

What if it is a heat pump with a Scroll compressor instead of a Reciprocating Compressor and does not have crankcase heaters?

Educate me Doug.

One other question to the group. When temps. outside are below a certain range
do not run the AC, correct, this is for a heat pump. Also, running in heat mode, when temps are below a certain range, run in normal cycle or em/aux for testing? All this is within SOP.


What do you mean by “not on”? Only if the power has been turned off to the unit is there a problem.

A scroll compressor can handle just about anything passing through it and should not be affected by the cold. It will make one heck of a noise when it starts up from the oil passing through the scroll though.

You should test the heat pump in both the heat pump mode in the auxiliary/EM heat load separately. When you test the heat pump you should be sure that the auxiliary/EM he is not on. You may need to turn off the breaker, or make sure you don’t turn the thermostat up more than 2° from an achieved setpoint (unit being off).

Running a heat pump in cold weather is never a problem as it is designed to operate in both heating and cooling (which it does every 45 minutes or so for defrost) in the winter. There is an accumulator in a pump that collects oil and returns it to the compressor at a slower rate to prevent potential damage to a reciprocating type compressor.

Well I am kinda up to speed on scroll pumps now, thanks David.
I made the assumption that Gary meant that the power was completely off to the unit, I see that that may not be the case.

I assumed that too, but then wasn’t sure.

It should be noted that there is always a potential to wash out the compressor oil on startup of a cold compressor. It will all come back so long as there is not a problem with the refrigerant lineset (split system only). We may not know of this potential problem as it is not something we normally look at and evaluate.