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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8164
Experience:  Furnace, A/C and heat pump specialist.
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607c ifm will not shut off

Customer Question

607c ifm will not shut off
Submitted: 1 year ago.
Category: HVAC
Expert:  airheatman replied 1 year ago.

Problem is going to be a bad fan control board or bad controller built onto end of motor.Do you have a multi meter for troubleshooting?

Customer: replied 1 year ago.
I changed the defrost control board and the ifm board, this is a Bryant/carrier 2 ton pkg heat pump and yes I have a multimeter the fan still runs when you disconnect the 24vac green wire from the thermostat to the low voltage green wire hookup inside the pkg unit. I looked at the ladder diagram and all the relevant relays are on the circuit boards as far as I can tell. I'm thinking maybe some snap disc for the emergency heat circuit is stuck thinking it has to remove residual heat from the air handler next to the coils and it won't allow the fan to deenergize
Customer: replied 1 year ago.
runs fine in cooling mode, hot gas reversing cycle is fine, defrosts fine , fan just never shuts off
Expert:  airheatman replied 1 year ago.

OK looks like the unit has a motor that is high voltage powered but low voltage controlled. Often the contacts in the bell on end of motor will stick.

Locate the low voltage wires from board Brown COM and the wire from LOW terminal on board. Disconnect those 2 wires and see if fan stops.

Customer: replied 1 year ago.
This sounds good, I'll try it tomorrow, I went to hvac school but it's been 15 years since I worked in the trade and lots of things got converted to circuit boards from old school relays. motor has common and 4 speed wires coming out so what you're saying is there is a relay in the motor itself powered of the ifm board's 24vac that may be stuck
Expert:  airheatman replied 1 year ago.

Yes there are contacts in the controller on motor itself for speeds controlled by low voltage.

If we disconnect the low voltage com and speed and motor still runs, we know issue is in that controller on motor. If not lets find where we might be getting 24 volts to that LOW terminal on board.Possibly a sequencer or something in heat kit.

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