Heat Pump Defrosting Too Frequently


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Old 03-05-16, 12:38 PM
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Heat Pump Defrosting Too Frequently

Hello everybody,
I noticed my outdoor unit has been defrosting every other time it runs. In actual run time it's like every thirty minutes or so. It has been hovering around the freezing point for the last several days with high humidity levels but never has it defrosted so often in the past. The unit is a Trane XL 1200 3 and 1/2 ton. I'm wondering if my coil temperature sensor has become defective and the defrost control has gone into a default mode. Any ideas would be appreciated. Thanks
 
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Old 03-05-16, 02:10 PM
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Under those conditions I would say that's normal.
 
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Old 03-05-16, 03:04 PM
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thanks for responding
skaggsje I'll keep an eye on it when it's at that temp again and see what happens when it is drier outside. Just odd that after 20 plus years I never had that situation. It's 40 now and rising over the next several days. No defrosting going on now.
 
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Old 03-05-16, 06:01 PM
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High humidity levels near the freezing point will allow ice to form quicker on the coils requiring more frequent defrost cycles.
 
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Old 03-06-16, 11:17 AM
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Hi Pete, my unit defrosted last night at 40 degrees outside. I'm sure that is not normal for my unit. It defrosted this morning at about 35 degrees which I can understand but not 40. It is a demand defrost and in the past I thought I was going to have to force a defrost when the coils were really iced up, but it finally kicked in. Something has changed in the demand defrost system. Need some kind of flow chart to trouble shoot.
 
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Old 03-06-16, 11:53 AM
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You'd need to post a make and model number for the condensor unit.

Frosting is not only based on ambient air temperature. It depends on dew point.

The refrigerant in a heat pump runs up to 20 degrees colder than the outside air. If this temperature is below the dew point of the air and below the freezing point... you get frost.
This can typically happen near or just below 40 degrees with humidity levels over 70%. As the outside air gets colder the humidity gets lower and frosting diminishes.
 
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Old 03-06-16, 03:15 PM
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Trane Model #TWX742A100A1 Serial#B44271338
Tested the thermistors today and they were close to the temp/ohms chart.
I get what you are saying about the dew point and Freon temp.
When I checked the coil sensor it was partially hanging out of the copper tube
 
 

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