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Old 04-15-2018, 11:42 AM   #1
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Why wont my heat pump compressors come on (predictably)?

I have Coleman AC units which also function as heat pumps. They both work really well when the compressors turn on, blowing very warm air, even when itís quite cold outside, but half the time the compressors donít come on, or they turn off at some point, just leaving the fans blowing cold air.

I canít find any consistency about when they do it. Iíve definitely determined that it isnít outside temperature related, or EMS load related. Also, they come on reliably when in AC mode.

Iíll be happy to forget about this when it finally warms up in Missouri, but right now itís driving me nuts!
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Old 04-15-2018, 11:57 AM   #2
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"Heat pumps will not operate below a certain outside temp ; 40/45 f.
Nature of the beast."


I'm sure you mean that below certain temps, there is not enough heat in the outside atmosphere to warm the refridgerant. If the outside air cannot warm the refridgerant, the inside unit will produce no heat.
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Old 04-15-2018, 12:32 PM   #3
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Whenever my compressors are on, they produce (pump) a surprising amount of heat. The trouble Iím having is that they are sometimes not coming on.
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Old 04-15-2018, 05:09 PM   #4
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Your heat pumps won't come on unless the inside temperature sensors indicate a need for heat. Generally these sensors are located rather high in the coach where it's warmer and the warm air blown by the heat pump circulates and shuts the thermostat off. Locate the sensors and cover them up so the warm air gets to them more slowly, see if there is a difference.
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Old 04-15-2018, 09:47 PM   #5
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Quote:
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Your heat pumps won't come on unless the inside temperature sensors indicate a need for heat. Generally these sensors are located rather high in the coach where it's warmer and the warm air blown by the heat pump circulates and shuts the thermostat off. Locate the sensors and cover them up so the warm air gets to them more slowly, see if there is a difference.


When the inside temp drops below the setting on the thermostat the fans come on as you would expect. Sometimes the compressors come on too, and when they do the place warms up nicely. When they donít it just gets colder!
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Old 04-16-2018, 08:41 AM   #6
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When the inside temp drops below the setting on the thermostat the fans come on as you would expect. Sometimes the compressors come on too, and when they do the place warms up nicely. When they donít it just gets colder!
It sounds like either a problem with your thermostat or a bad control board in the AC unit. We had a control board go out on one of the Coleman AC units on our Adventurer. Sometimes the unit would work fine. Other times it wouldn't change from the cooling mode to the heat mode. When that happened the compressor would stay off if the actual temperature inside was below the set temperature on the thermostat. The fans would just blow around cold air. If the indoor temperature was close enough for the AC to come on it would, only it would be in the cooling mode rather than the heat mode.

In our case a new control board fixed the problem
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Old 04-16-2018, 12:55 PM   #7
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Heat pumps can and do "freeze up" and there is an internal temperature sensor to detect that. When the refrigerant action slows due to internal freeze up, it enters a defrost cycle in which the compressor shuts off but the fan continue. Once it stabilizes, the compressor will automatically restart. My home heat pump does the same thing.

If you find the heat pump compressor cycling repeatedly when it's not very cold outside, say 50+, you may have inadequate air flow through the unit, either externally or internally. Either one can cause premature defrost cycles.
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Old 04-16-2018, 01:15 PM   #8
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If your Coleman's are original, it's certainly possible the reversing valves are sticking. Do both units do the same thing (I.E., if both are in HP mode, do they both work/not work at the same time)?
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Old 04-16-2018, 02:52 PM   #9
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If your Coleman's are original, it's certainly possible the reversing valves are sticking. Do both units do the same thing (I.E., if both are in HP mode, do they both work/not work at the same time)?
If the reversing valves are sticking it's time for new AC units. Neither Coleman or any other after market parts supplier sell reversing valves for these units. Even if they did the price for a new valve, installation and recharging the system would cost about half the price of a new unit.

However the control board I mentioned in my previous post does control the reversing valves. If they fail they are available through Airxcel. The one for our AC unit was a little over $200.00. Fortunately Coleman covered it under warranty.
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