Heat Pump Issue, Outdoor unit (compressor) turns off prematurely

[DesertRat]

I live in the Phoenix, AZ metroplitan area and I have a strange issue with one of my home's heat pumps.

Here is the situation. The heat pump works great all summer long as an AC unit, no issues and keeps everything nice and cool. As a heating unit it has a quirk. It will heat just fine but occasionally the outdoor unit (the one with the compressor) will shut off prematurely. The fan/blower is still blowing and the indoor temperature is still lower than the target temperature on the thermostat. It will remain in this state for some time (at least an hour) then it will come back on. Of course during this time it is blowing cool air. The colder the outside air is the less this happens. I do not believe it is a defrost cycle issue because it does its periodic cycle reverse to defrost just fine. It also is not tripping the compressor high switch because I try to push that in and it doesn’t do anything. The outdoor units fan motor is fine; it doesn't turn off before the compressor causing the compressor to overheat. The whole outdoor compressor unit just seems to shut down for a while then come back to life.

Any ideas?

[HayZee518]

just a question: does your compressor have a crankcase heater?

[DesertRat]

I don't know, but I don't believe so. Its a scroll compressor if that helps.

[HayZee518]

my reason for asking about a crankcase heater is that the heater is used to keep the oil that travels with the freon, fluid. if the oil is sluggish then the compressor overload may trip. If it's setup as an automatic reset the when it trips and cools down, it will restart and trip out again, which will account for your short cycling. a scroll compressor is a helical gear type of compressor.

[DesertRat]

First thank you for your comments so far. If I get the make and model number this evening and call the manufacture tomorrow is that something they would know? Is this something that is visible if I look at the compressor housing? If I see a heater is it as simple as measuring the resistance to see if it has fried? Also can the oil become sluggish with an ambient temperature of 40F, that is how cold it was when this happened.

[HayZee518]

I don't see how at 40 degrees BUT, never assume something. I'm just trying to come up with ideas of why and how come?