blower fan stuck on


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Old 04-21-19, 04:29 PM
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blower fan stuck on

First post, looking for some help. I know another "blower fan stuck on" post, sorry!

Problem: Armstrong air unit, 15 years old. Blower fan was replaced probably 8 years ago. The main blower fan remains on, even with thermostat wires completely removed at main controller board in furnace. When I turn the main power switch on to the HVAC unit (with thermostat wires undone), the fan exhaust blower and main blower fan run, and stay running.

Things I've tried: I've removed all thermostat wires from the main control board to eliminate thermostat. I then bought a new Honeywell ST9120U1011 universal fan timer. Hooked everything up, excluding the thermostat wires; applied power to the HVAC, and same thing happened: both the exhaust fan and main fan turn on.

Some photos (old board, new honeywell, side pic of the fan (capacitor?):
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I read a lot about a fan relay switch getting stuck, but I cannot find one anywhere. Any ideas?
 
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Old 04-21-19, 09:57 PM
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Welcome to the forums.

the fan exhaust blower and main blower fan run, and stay running.
That should be a clue right there. You are talking about two different blowers. One stuck relay would not keep two blowers on. Your problem is a furnace board needs to be completely installed and wired correctly. Any open limit switch will keep both blowers running as an indication of a fault.

If the control board has a fault light on it...... it should be flashing a code.
 
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Old 04-22-19, 05:49 AM
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Thanks for the response!
Both the old controller board and the brand new Honeywell controller board act exactly the same when completely wired up. I do not see any fault codes blinking.

Is there a separate furnace board I should be investigating?
 
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Old 04-22-19, 01:44 PM
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Is the LED blinking anything ?
Check for 24vAC between R and C..... is it there ?
 
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Old 04-29-19, 12:34 PM
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Main control board flashes a green light heartbeat. There's a green light that flashes up near the gas lines, 4 times.

Assuming I'm using my multimeter correctly, I'm only reading ~300mV across those two lines, at the main control board.
 
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Old 04-29-19, 02:41 PM
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Four flashes near the gas valve ? Is it right on the valve ?

I think the model number of the furnace is going to be needed.
There is a pair of yellow wires that connects to the board near the fuse. Check them for 24vAC.
I'd imagine you'll find that present which points us to an open limit switch.
 
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Old 04-30-19, 07:59 PM
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Thanks for the feedback everyone. I gave up and called in a professional. It was some sort of temperature sensing valve (~$18). It was telling the system that the temperature was hot and the fans needed to run to cool the system down before shutting off.
 
 

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