I think I see your problem

Would low coolant do that? Like when an A/C unit ices up? Just curious.
Not likely, because it would still go into hot gas defrost cycle.

A heat pump will build some frost on the coil when it's pretty cold out. The control board will try to initiate a defrost cycle on a timed basis if the coil sensor does not terminate it. What it essentially does is to switch the reversing valve back to normal A/C mode for a short time so the hot discharge gas will flow through the outside coil and melt any frost.
 
Did anyone else get a completely reasonable hankering for one of these ?

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Not likely, because it would still go into hot gas defrost cycle.

A heat pump will build some frost on the coil when it's pretty cold out. The control board will try to initiate a defrost cycle on a timed basis if the coil sensor does not terminate it. What it essentially does is to switch the reversing valve back to normal A/C mode for a short time so the hot discharge gas will flow through the outside coil and melt any frost.
Mine is a high efficiency Lennox. When it hits the defrost cycle it slows the air handler. It also sounds like a freight train outside. This is odd to me because it's normally super quiet.
 
Mine is a high efficiency Lennox. When it hits the defrost cycle it slows the air handler. It also sounds like a freight train outside. This is odd to me because it's normally super quiet.
Yep, when that vale reverses you get a major "woosh" outside. But when that hot gas flows through the coil, the ice melts in seconds.
 
Yep, when that vale reverses you get a major "woosh" outside. But when that hot gas flows through the coil, the ice melts in seconds.
Yeah it doesn't stay on defrost long. We had some ice fog the other morning and it did cycle a good bit. I wonder if that puts strain on the system? I thought about switching it over the the strips for a while.
 
Yeah it doesn't stay on defrost long. We had some ice fog the other morning and it did cycle a good bit. I wonder if that puts strain on the system? I thought about switching it over the the strips for a while.
Many systems try to initiate a defrost cycle every 90 minutes unless the coil sensor cancels it. The compressor is more loaded during defrost cycle, but it is a necessary function.
 
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