View Full Version : Emergency heat is coming on when A/C is running. WHY?

Jul 22, 2009, 11:17 AM
I have a coleman heat pump.
Outside unit mod# 3330a901 SER# 10810578
Inside unit code & ser# 028261474 mod# 3300-815
DOE output capacity BTU 53,000
I have the original coleman thermostat with mercury bulbs attached to a lever.

I live in north central Texas where it gets over 100 degreesF.

I have a new fan motor on the condenser unit.

I had freon filled about a week ago.

While the a/c is running the compressor and cond fan will stop and cause the emergency heat to come on. The insider blower will continue to run until I turn it off. The emergency heat light will stay on and will not turn off for about 20 minutes then I have to turn the emergency heat switch on and off to get the light to go off. After that the a/c compressor will come on again and sometimes it will run for 20 minutes sometimes for an hour and this process will happen again. This morning after this process I turned the a/c on and it ran for about an hour and 10 minutes and the evaporator coil froze up.

Is there a relay or switch outside that might be failing or overheating and causing this to happen? Or what could be causing this to happen? Can I disconnect the emergency heat system so it will not heat my house in the summer?


Jul 22, 2009, 12:20 PM
The emergency heat should not come on if the thermostat is calling for cooling.

The reason could be

The thermostat is defective. (not likely but possible)
The low voltage wiring has a short circuit. This could be anywhere along the low voltage wiring from the thermostat to the inside unit and from the inside unit to the outside unit. Anywhere along this path a problem could cause a short circuit.
If the outside defrost timer/control is defective it could send a signal to the indoor unit to activate the emergency electrical resistance heater(s).

I would start by checking the above first then report back. Note if you do not know what you are doing with the low voltage lines or if you do not have the proper tools I would suggest you contact a professional. It seems you have had a lot of work already done on your unit and it is possible that during one of the repairs something may have happened to cause this problem.