Intermittent air handler fan

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Old 09-08-08, 02:48 PM
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Intermittent air handler fan

The fan on my Frigidaire air handler, Model B3BM-030K-AB will come on if turned on manually, but will only occasionlly start when set on auto cool.

I have swapped the thermostat with one of the same model that I know is ok, and still have the problem. I have deduced from other posts that it must be the fan delay relay.

Can anyone tell me where the relay is on this air handler, and can I change it out. I don't see any obvious relays other than the ones on the controller circuit board.

Also, there are two relays on the circuit board. Wires to the fan motor are connected to one relay, there is nothing connected to the leads on the other relay. I am wondering if switching the wires to the other relay would bypass the delay.

Thanks for any help you can give me.
 
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Old 09-08-08, 04:39 PM
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I looked at the wire diagram for your unit, and I only see one relay on it.

The fan always runs when you turn the tstat to fan ON, but when in Auto, and call for for cool, it cycles on and off?

do you have a meter to check for power?
 
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Old 09-08-08, 05:07 PM
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I looked at several diagrams. 5Kw, 8Kw, and 10Kw all show two relays on the board.

Hope this link doesn't ask for login:

B3BM Air Handler with Factory Installed Heat, 8kw, 10kw

I keep thinking of the stat even though you changed it out.

Setting the fan to on closes a relay in the stat to energize the G terminal. In Auto, the call for cooling energizes both Y and G.
 
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Old 09-08-08, 05:48 PM
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Without being able to put a meter on it, I'd say the relay is bad, which means a new board. You can temporarily run it with 'fan on'.
The relay's NO contacts are what close to bring on the high speed of the fan when calling for cooling - power coming back from the stat on Y.
The relay's NC contacts bring on the blower through a time delay built into the board when the stat is calling for heat using W. The delay allows the strips to heat up so it doesn't blow cold air at first. Also, the low speed would be energized for heating (or maybe medium).
I'd guess the 2nd relay on the board is the time delay relay, and connected to the board - soldered.
Time for a new board...
 
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Old 09-16-08, 11:03 AM
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Thanks everyone. The new board fixed it.
 
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Old 09-21-08, 01:15 PM
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Occasionally I'll get one right doing it long distance, sight unseen... Beer 4U2
 
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