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Carrier furnace with electric heat pump-turns on and off before set temp

dctaz37

Premium Member
Joined
Jan 21, 2021
Messages
3
Location
Ontario
Model Number
FB4A, 38QRA
Age
More than 10 years
Hello, I have a Carrier furnace FB4A with heat pump model 38QRA. The unit is getting up there in age and the only service I've done is to replace the contactor about 2 years ago. In the beginning of the summer the AC kept running regardless of the setting on the thermostat.

The thermostat is the old style with the mercury in the glass to make the contact. I set the thermostat to the end so the AC shouldn't engage, shut the furnace breaker off, waited an hour, then turned it back on but the furnace started. After shutting the furnace breaker off over-night, it has run properly for the summer.

The same thing happened yesterday so I set the thermostat to the end so the AC shouldn't engage, shut the breaker off. This morning I turned it back on and the furnace started then stopped and it kept cycling on and off. I turned the AC down for a few minutes then to a higher temperature to shut off and it cycled until it shut off. It was okay for a few hours but then started cycling on and off again.
 
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