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My dads totally sick, so Im trying to fill in but we dont specialize in HVAC or any one type of service, more overall general stuff. Right now Ive been trying to fix this guys electric funace and I dont know what else could be causing it not shut down. I replaced the blower relay, the sequencer, and the thermostat. I fixed the original problem which was the heater coils would energize but the blower would not turn on. But now the furnace will not stop heating after the thermostat turns off. This happens at random, sometimes it shuts down and sometimes the blower & heater keep running. Also if I switch the fan to the auto position (which is high speed) it will trigger the furnace to shut down. The furnace is electric and 25 years old. Does anyone know why it wont shut down?
 

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Sounds like a lot of new parts. What happens if you disconnect the thermostat wiring where it connects to the unit?....lets start there.

If the heat still runs you can obviously rule out the thermostat, or a short in the wiring from the thermostat. At that point you would know the problem is within the actual unit.

If the coils are still energized at that point you may have accidentally hot-wired them when you replaced the controls.

Do you know the sequence of operation for the unit? What causes the blower relay to pull in?

The auto position on the thermostat would cause the fan to cycle on and off with calls for heat. It works in conjunction with a switch or setting in the thermostat that sets it to "electric" heat as opposed to "fuel"....again, I don't know the whole setup you have here, but in most cases with electric heat you're going to want electric and auto...this means the thermostat sends a "G" signal on a call for heat to start up the fan, and breaks this call when satisfied. This is usually the problem when your heater elements are getting hot but the blower doesn't come on- home owners are notorious for changing their own stats and "overlooking" the electric heat setting (all stats I know of come factory set to "fuel")

-Jason
SUREFIRE Mechanical- Long Island Air Conditioning Repair Experts
 

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My dads totally sick, so Im trying to fill in but we dont specialize in HVAC or any one type of service, more overall general stuff. Right now Ive been trying to fix this guys electric funace and I dont know what else could be causing it not shut down. I replaced the blower relay, the sequencer, and the thermostat. I fixed the original problem which was the heater coils would energize but the blower would not turn on. But now the furnace will not stop heating after the thermostat turns off. This happens at random, sometimes it shuts down and sometimes the blower & heater keep running. Also if I switch the fan to the auto position (which is high speed) it will trigger the furnace to shut down. The furnace is electric and 25 years old. Does anyone know why it wont shut down?
Sounds like you got your wires crossed. You gotta proof the air for heat coils. Sequence this.Heat call W should turn on fan first and proof it before W is allowed to start heat call. Either way sounds like the board.
 

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Hopefully, it was figured out 7 years ago when the OP made the thread.
 
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