Heat Pump Problem

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  #1  
Old 12-11-02, 12:15 PM
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Heat pump coils frozen when *heating*

Hi,

I'm at my girlfriend's house and we're on the tail end of a freezing rain. I just went out to chip the ice off the top of the outside heat pump unit and noticed that the inside of the coils was caked with 2-4 inches of frosty white ice. I guess it came from misty rain getting sucked through the coils while temperatures were below freezing.

What should I do about this? Would running the AC for a few minutes heat up the coils enough to melt the ice? Since it's only about 33 degrees outside, I can't just pull the circuit breaker and wait for the ice to melt.

Any suggestions or advice would be greatly appreciated.

Thanks!
 
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  #2  
Old 12-11-02, 12:24 PM
rclhvac
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If you have elcetric backup -goto emergency heat. Your defrost circuit may not be working properly. The defrost mode runs the unit in a/c without the outdoor fan runing.
 
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Old 12-11-02, 05:02 PM
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will running in emergency mode automatically kick in the defrost cycle, or should the defroster be running regardless? If the latter, I suppose she'll have to get it fixed. Is that usually an electronic problem or a mechanical one?
 
  #4  
Old 12-11-02, 06:09 PM
rclhvac
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Emergency bypasses heat pump & goes straight to electric heat.
Defrost is automatic while heat pump is running
 
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Old 12-14-02, 08:11 AM
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It's 3 days later and I'm back at her house. There is still ice on the coils. It's .5 - 1.5 inches thick and it covers the entire wall of coils on all four sides, except for the top inch or so (where it's probably not cold enough to make ice). The ice seems denser and clearer today than last time. Perhaps the frosty white was just a surface layer caused by the misty freezing rain we were having.

I've switched to emergency heat as suggested, but I'm not sure why this would help. The heat pump was still heating the house with the ice. Perhaps the suggestion was in case the ice was preventing it form doing its job. Or will the ice cause it to overload?

I'm considering running the AC for a few minutes. I'll keep my eye on it to see if it makes any indications that it's melting (dripping, cracking, creaking). If so, I'll run the AC unitl it's all gone. If not, then maybe the defrost and the AC are busted.

Am I missing or misinterpreting anything?

Thanks again!
 
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Old 12-14-02, 09:05 AM
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Update

Ran the AC for about 30 minutes. Worked like a charm. There are still some chunks of ice sitting close to the bottom, but they have at least fallen away from the coils. They're not really in the way of air circulation.

So, at least the unit is able to circulate in that direction, but the defroster may still be broken. What mechanics are involved in the defroster? Does the compressor actually run when defrosting? Is there a controller that could be fried? Could there be a problem with line pressure?
 
  #7  
Old 12-14-02, 01:37 PM
rclhvac
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Newer units have a defrost circuit board (different styles in different makes). When the unit starts to ice- the low temp from ice forming closes a sensor curcuit. When the timing of the defrost board checks for ice and the sensor is closed- it switches into defrost mode. The outdoor fan stops running , and the unit switches to a/c. Electric heat comes on to temper air to room. As a certain amout of time passes or the sensor opens, the unit switches back to heating.
You were probably keeping warm with the electric strip heaters -& not the iced up unit. That's why i said to go to emergency heat untill it could be checked or repaired.
In emergency heat the thermostat only turns on the electric heat & leaves the outside unit off
 
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Old 12-14-02, 08:05 PM
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ok, that makes sense. The fan has been running outside, but you may be right that the emergency heat units were doing all the work.

I'll tell my girlfriend to have someone come look at it if/when it ices up again. I suppose it would be hard for a service tech to diagnose the problem if there is no ice to trigger the defrost cycle.

Thanks for all your input!
 
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