Heat pump defrost


Old 12-08-13, 02:50 PM
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Heat pump defrost

My upstairs heat pump has frosted up today and never seems to go into defrost. Today was sleet in morning and now is rain. I switched over to E heat for now.

Just wondering how the heat pump detects that it should defrost. I've seen it do it before but it seems to wait till the condenser is fully blocked.

Also, how does the defrost work? I see the outside fan turn off and the compressor runs then a little time later the frost starts melting.
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Old 12-08-13, 07:01 PM
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You may have a failing defrost timer or sensor.
Post the make and model of your outdoor unit.
Old 12-08-13, 11:58 PM
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Think I found out why. My heating elements inside the attic unit are not coming on. I did see the outside unit go into a defrost cycle but the frost is so thick it will not clear. When it goes into a defrost the air temp blowing out one vent was 57 degrees.

So I guess a defrost cycle just switches the heat pump into AC cooling but turns off the outside fan and should turn on the heat strips.

I also guess it's just a timed defrost cycle since it does not clear the frost.

I will have to get a meter up into the attic and find out why the heaters are not coming on. Are relays a common failure?
Old 12-09-13, 06:44 AM
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I took a meter up to attic and it looks like both heaters are burned open. They have 240 volts on the terminals. I did an ohm meter test on them and they look open. How could that happen? My blower motor did burn out this summer and was replaced. The outside unit is a Comfortmaker N4H324AKE1000.
I think the unit still has warenty so parts will not cost me but the labor will probably be $200.

Anyway, even the down stairs unit got covered with ice blocking the fan. That unit is a Trane R22 old unit. We had rain all day and all night right around 32 degrees. Should I consider building a roof over the outside units to prevent ice build up again.

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