08:18AM | 01/15/07
Member Since: 01/14/07
2 lifetime posts
The house I bought has a Comfortmaker Heat Pump and a Lennox gas furnace combination controlled by a Lemmox FM21 and Lennox thermostat; refrigerant coil on "heat" side of furnace. I was under the impression that when the temperature was below 40-degrees, the AUX Heat light would display (it does), the gas furnace would light (it does), and the Heat Pump would shut down (it doesn't). First, should the heat pump turn off when in AUX heat mode?

Second, I was also told I could use the gas furnace exclusively without the heat pump by switching to Emergency mode. I did so while in AUX mode (Heat Pump and Gas furnace on) and it did shut down the heat pump. However, when the heat cycle ended and restarted later, STILL in Emergency mode, the heat pump restarted! Am I correct that I should be able to run gas furnace exclusively by switching to Emergency mode? If so, what is wired incorrectly? Any help would be appreciated. Thank you.

Thanks ... Rich


12:39PM | 01/26/07
Member Since: 01/14/07
2 lifetime posts
Thanks for your reply, although it is not completely understood. I assume when you suggest to keep HP running during the winter, you mean don't turn thermostat to Emergency Heat which shuts down HP BOTH above 40-degrees AND below 40-degrees. If so, I am comfortable with your answer. This is different from Auxillary Heating where the Lennox FM21 Control between gas furnace and HP should turn the HP on above 40-degrees and let it OFF when outside temperature is under 40-degrees using the gas furnace instead.

Anyway, I did remove the "hard-wire patch" some installer did that always kept the HP running regardless of the outside temperature. Now my system runs as designed, or at least how the FM21 controls says it should run, i.e., above 40-degrees run HP only and under 40-degrees run gas furnace only.

End result as far as starting and stopping the compressor to me seems to be the elimination of the number of starts and stops when the temperature outside is under 40-degrees -- that should be good as your answer implies.

If I am completely off base, please advise.

Thanks again.

Thanks ... Rich
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