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Gaztech, HVAC Technician
Category: HVAC
Satisfied Customers: 485
Experience:  Owner at Gaztech
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Indoor fan won't shut off unless I use the circuit breaker.

Customer Question

Indoor fan won't shut off unless I use the circuit breaker.
I have a Carrier split system gas/electric. The indoor unit is a model 58EJA100 and the outdoor unit is 4 ton model AC1AN048. Starting this past Monday we had a heat wave (105F) and that’s when the problem started. I replaced the circuit board. The heating on the circuit board failed this past winter, thinking it was causing the fan problem. With the new circuit board the heating works fine but the fan runs continuous.
There is no fan relay (controlled by a circuit board) only a capacitor on the indoor blower. The outdoor AC unit works fine and will energize on a call for cooling from the thermostat.
The existing thermostat was old so I tried replacing it but it still didn’t solve the problem, the fan runs continuously. All the obvious was checked on the thermostat, it’s in the Auto Fan mode. It makes no difference if the thermostat is “off” or set to “Cool” the blower fan will run continuously.
Any suggestions on how to get the fan to shut off properly?
Submitted: 1 year ago.
Category: HVAC
Expert:  Gaztech replied 1 year ago.

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Customer: replied 1 year ago.
Please start
Expert:  Gaztech replied 1 year ago.

have you tried disconnecting the wire on G terminal directly at the furnace control board ?

If fan shuts off this would indicate that you there is short on that wire

Expert:  Gaztech replied 1 year ago.

Did you find the problem?

Customer: replied 1 year ago.
I give that a try in the AM, too hot in attic now. Sorry can't do a phone call now, my voice is shot. Some kind of summer bug.
Expert:  Gaztech replied 1 year ago.

OK, let me know what happens.

Customer: replied 1 year ago.
Gaztech,Thanks for the suggestion,Initially before I replaced the thermostat, I tried removing the wire on the G terminal at the thermostat, but the fan kept running.I tried removing the wire on the G terminal at the furnace circuit board and the fan goes off. So it appears there is a short somewhere, which I have not yet found.The fan wire (G) from the circuit board goes to a smart vent system (economizer) that controller box has 5 different brown thermostat cables going into it. It took some time but I finally was able to track down a wiring diagram for the smart vent system. There are 2 small fuses inside the controller box and both are okay. It’s taken some time to identify which cable is going to the main thermostat. There is a 2nd smart vent thermostat also. The fan wire from the furnace circuit board to the smart vent controller tested good. It was a short run.I suspect that a wire from the main thermostat to the smart vent controller is where the short is, or at least that will be my 1st try before moving onto the smart vent wiring. Is there an easy way to test each wire for a short without doing a trial and error? The furnace is in a very tight place in the attic.Also I realize with the holiday weekend you may be off-line for a while.Carl
Expert:  Gaztech replied 1 year ago.

Hey I am here, just reading your update

Expert:  Gaztech replied 1 year ago.

Test wires is done with a ohm tester and disconnecting the wires at both ends and test them one by one.. get it?

And also the economizer might have a bad relay and it is calling to turn fan on