Furnace fan stays on

Old 09-28-03, 04:20 PM
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Furnace fan stays on

I found my thermostat was burnt. When I looked inside the thermostat I think it was the regulator of some sort (a component with a heat sink on it) that was burnt. Ever since I couldn't turn off the fan. I installed a new thermostat, I tried to adjust the temperture up and down, turned the fan switch off, even disconnected the wires to the thermostat, none of these worked - the fan still on. I can only turn off the fan by turning off the breaker switch.
I opened the furnace cover and looked in the Fan Control Unit (I am not sure if this is the correct name for it), I didn't see any obvious problems, like burnt components and wires and the two relays seem to be in their normally open position. I used an ohm meter to measure the colored wire (Y, G, R, W) from the thermostat at the connectors on the PCB, they were shorted. I made sure the wires themself were not shorted (inside the wall) by disconnecting the wires at the connectors and they were not. My questions are:
1. Is the problem with the Fan Control Unit?
2. Did the faulty Fan Control Unit cause the thermostat to burn out or the other way around?
3. Is the Fan Control Unit an expensive item?

Manufacturer: Payne
Model #: 394JAWC48C65 (forced air)
Year made: 1987
80,000 BTU
Fan control unit p/n: HH84AA-011

Thank you for your help in advance.
Old 09-28-03, 04:30 PM
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Sounds like your board is bad - do you have a/c ?
Any water leak into heater- main cause for board to go.
Need alittle more info
Old 09-28-03, 06:22 PM
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Thanks for the reply. I do have a/c. When I opened the control unit, there was no moisture or water stain present. I went to check again after I received your post, the unit and its surrounding area was dry.
I live in San Francisco Bay Area. The climate here is cool and dry. I use my a/c average 5-10 days per year. I hardly used the a/c this year.
I do agree with you and suspect the control unit's board is faulty. Is there any way to confirm or check if the board is bad, other than trying it with a new one??

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