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Old 01-30-2013, 11:53 AM   #1
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Troubleshooting a Heat Pump


Need some basic guidance troubleshooting a heat-pump. Noticed that the temperature rise was only only 1-2 degrees, on mild days, and that the system was having to engage the resistance strips to produce any real heat, even on warm-ish days. Being the original owner, I know its performance characteristics (will usually not require resistance heat until -15C), whereas suddenly, it couldn't keep the house warm at 0C / 32F.


Hereís some possibly useful information:


Breakers all checked out good. None had shut down.

Outdoor compressor starts and runs normally.

Indoor furnace fan is also working normally.

Filter is new, and air-flow is unobstructed.

When operating in heat-mode, the large, insulated, copper pipe connecting the exterior heat-pump to the interior furnace/air-exchange is as-expected, hot to touch. This would seem to indicate that the compressor is doing its job and getting adequate heat from outside to bring inside for air-exchange.

Unfortunately, heat pump is mounted on the roof which is very difficult to get to right now. Thus I'm simply running on resistance heating and have locked out the heat-pump, until spring. Or until a better idea comes along.

Given this limited information, is it possible to assess the likelihood that the problem is low refrigerant, a bad reversing valve, defrosting, or other electronics?

Brand of the unit is ďAire-FloĒ which I believe is a builder brand of Lennox. Unit is 9.5 years old. Its needed a newblower motors, and a heat sequencer, which isnít bad for 9.5 years.

Would running it in cooling mode at this point add to the diagnostics? Current temperature is 8 Celcius / 46 Fahrenheit.

Thanks for any suggestions.

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Old 01-30-2013, 02:28 PM   #2
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Troubleshooting a Heat Pump


Looks like your system is working the way it should be.

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Old 01-30-2013, 02:50 PM   #3
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Troubleshooting a Heat Pump


Hi thanks for your suggestion, but let me clarify:


Behavior throughout the past 9 years:
At about 0C (32F) outdoor, heat pump would fully heat house, with no need for backup/resistance heating.
Temperature rise was about 4-6C measured at air outlet .
Secondary (emergency/resistance) heat could be kept locked out (upper balance point was -5 and lower balance point was -13)



Recent behavior:
At about 0C (32F) outdoor, unit was not supplying much heat at all. Temperature rise was about 1 degree or less measured at same air outlet. In order to heat house, needed to adjust the upper balance point so that it permitted resistance heating to come on at any temperature).

Thanks again.
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Old 01-30-2013, 05:10 PM   #4
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Troubleshooting a Heat Pump


Close to 32F heat pump will be using a lot o the aux heat. You said the suction line is hot to touch. This means the heat pump is working. But you can still check the refrigerant level. I think the outdoor temp is too cold for the heat pump.
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Last edited by JJboy; 01-30-2013 at 05:16 PM.
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Old 01-30-2013, 07:18 PM   #5
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Troubleshooting a Heat Pump


Could be low on charge. Slightly low on charge the large pipe will often still be hot, but the small line will be almost cool to the touch.
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Old 01-31-2013, 10:32 AM   #6
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Troubleshooting a Heat Pump


Hi JJ, you mentioned, ďClose to 32F heat pump will be using a lot of the aux heat.Ē That probably holds for the heat pumps typical of your locality (I see youíre in Texas). Iím in Montreal, and the pumps weíre sold are designed for lower operation. Iíve previously measured that it would keep the house temperature constant and not require any aux heat down to -15C. The installer set it up to lock the resistance heating out above -7C and lock the compressor out below -13.

That being said, yesterday we happened to set a record high temperature for January 30th in Montreal and the temperature reached almost 10C (50F). On heat-pump alone, suddenly I was getting very healthy 16degreesC temperature rise.

Would a low coolant level manifest itself like that? Works great in mild weather but rapid drop off in ability to function in cold weather?
The other alternative Iím considering is that the defrost isnít working. I recall the original service guy who went on the roof explaining that it had a switch on the unit (on the roof) that you selected to defrost every 30, 60 or 90 minutes.
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Old 01-31-2013, 10:58 AM   #7
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Troubleshooting a Heat Pump


You need somebody to check is the system is under charge or leaking and defrost board.

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