Exhaust blower runs all the time

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Old 09-18-07, 04:29 AM
K
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Exhaust blower runs all the time

I have an Arco-Aire Gas furnace with A/C, Honeywell programmable thermostat and Honeywell ST9120C4016 control board.
The exhaust blower runs all the time - when A/C is running, when thermostat set to off, even if I remove the thermostat from the wall base.
There's three DIP switch's on the control board. I haven't tried changing those, but were thinking they adjusted the timing of the main air handler fan, not the exhaust fan.
I've checked the wiring and all seems to be wired correctly. The A/C compressor and air handler fan run correctly. Any advice as to why the exhaust fan would run all the time?
 
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Old 09-18-07, 07:52 AM
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I am leading towards the relay on the board is stuck for the inducer motor.

You are almost best to just have the board replaced.

You could try tapping on one of the black relay box and see if anything happens.
 
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Old 09-18-07, 12:12 PM
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Lightbulb honeywell boards

Originally Posted by kcnchester View Post
I have an Arco-Aire Gas furnace with A/C, Honeywell programmable thermostat and Honeywell ST9120C4016 control board.
The exhaust blower runs all the time - when A/C is running, when thermostat set to off, even if I remove the thermostat from the wall base.
There's three DIP switch's on the control board. I haven't tried changing those, but were thinking they adjusted the timing of the main air handler fan, not the exhaust fan.
I've checked the wiring and all seems to be wired correctly. The A/C compressor and air handler fan run correctly. Any advice as to why the exhaust fan would run all the time?
You're right, the dip switches have nothing to do with the exhaust motor, they are for the air handler fan motor. Is this a new problem? Reason I ask is some programable thermostats are caled power stealing models. They will have a trickle circuit through the heating terminal that could fool the board and cause the exhaust fan motor relay to pull in. Otherwise, it may just be a bad board as suggested by Jay. Honeywell makes a universal board that will replace yours. It's ST9120U1003, $85 plus shipping from aronld's hvac parts online. [good price ]
 
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