Heat pump condensers freezing over

sktn77a

Hello all: Having a strange problem at our house. It's on a lake in Virginia (humidity?) and when the weather gets cold (freezing or just above) both of our outdoor heat pump condenser units are freezing over. I could understand it being a fault if only one were freezing over, but both of them? They are both Carrier 38YCC36 (3 ton) outdoor units new in 2005 but not heavily used (the house was someone's vacation home until we bought it last year). We had the charge checked and the defrost board replaced on the downstairs unit.

Any ideas?

AllanJ

Are there any adjustments for "calibrating" the defrost cycle? (refer to instructions)

Did the serviceman who replaced the defroster board verify that the defrost cycle was actually working after that?

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beenthere

Check what the defrost timer is set to. If its at 90 minutes, set it to 60 and see how it does. If 60 set it to 30.

High humidity will cause heavy freezing.

sktn77a

There is a defrost cycle adjustment but I don't remember what it is set at. I'll check on that.

sktn77a

Checked the defrost cycle times yesterday. There are three choices - 90min, 60min and 30 min. Both condensers were set on 30 min so unless neither consenser is working properly (Highly unlikely, I would think, on both units), any ideas what else could cause both systems to freeze over? (They weren't solid blocks of ice but they were pretty much covered with frost, top to bottom and inside to outside and not working efficiently (aux heat coming on, outside temp above freezing).

Thanks,

joecaption

Dirty inside filters, dirty slant coil in the air exchanger?
Just a guess.

beenthere

Yep, check indoor coils and air filters. may have a leak in both units. Seldom happen to 2 at the same time, but it is possible. Are you still having lots of high outdoor humidity days?

sktn77a

Thanks guys. Temps have changed a little - colder and, therefore, maybe drier? The units weren't freezing over this weekend but the pipe coming from the outside coil to the compressor had frost on it. Filters are clean; outside coil looks clean (can't really see between the fins but inside and outside are clean as a whistle). Can't get to indoor coil but it was inspected by the HVAC company twice last year and has had clean filters ever since.

Guess I'll have to call them out again (sigh).

Keith

beenthere

Not unusual for that pipe to have frost on it when its colder outside.