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Need help troubleshooting attic fan

Posted by mjhjea (My Page) on
Tue, Aug 2, 11 at 10:21

Hello. The original whole house fan that was installed when we built our home (1994) quit working. I found a new motor with same physical dimensions except slightly bigger in HP. Original motor was 800 RPM and the new 1070 at high speed. I installed new motor with original fan blades, however, there is very little puling of air through the house. Fan blades were installed correctly and I've tried switching the wiring for medium and slow speeds, still no pulling of air. Rotation of shaft is also correct and when I hold a piece of thread under the fan, it does not pull it up until I hold it very close. Our original fan would pull ashes out of the fireplace if we had no door or window open, but nothing with new motor. Also, the new motor seems to get extremely hot with little use. I cannot figure out why there is a problem or what else I can try. Can someone please offer some insight? Thanks so much, Mark


Follow-Up Postings:

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RE: Need help troubleshooting attic fan

Well here are some thoughts. You must make sure you have enough openings in the attic to allow the air to pass through ie gable or ridge vents of suficient size. Make sure those vents have not been blocked. Also you must obviously make sure a window or maybe 2 are open.

Possibly, at the higher fan speed your fan blades are stalling. Try your thread trick and see if it starts to rise when you turn it on and then drops.

Also, even though it says it is a higher RPM, is it actually higher? If the new motor is defective (high heat symptom) maybe you are not getting the full RPM.

I'M not an HVAC tech but I do stay at Holiday Inn Express


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RE: Need help troubleshooting attic fan

I thought new motor was defective so I exchanged it and I'm still dealing with same issue. I also have plenty of ventilation with my full ridge vent as the original fan worked phenomenal before it quit on me. I remember before how the original fan would suck a cracked door open, it had that much force. But with this new motor, I can barely feel anything. I'll open only one window to check air flow, but feel nothing. The luvers open up on the ceiling panel when fan is on, so I know fan is at least trying to do what it's supposed to. I just don't understand the situation. If a motor is turning the shaft/blades, why no air being pulled in from the outside?


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RE: Need help troubleshooting attic fan

Is the fan slipping on the shaft? Is a running capacitor required for the new motor and do you have the correct size?


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RE: Need help troubleshooting attic fan

Hi. Fan is not slipping on shaft. I have the correct capaitor for the motor.


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RE: Need help troubleshooting attic fan

I have to think that you don't have enough venting capacity in the attic. Either the ridge vent or soffit vents have become partially blocked. Soffits can get blocked with insulation. Yes, soffits are intakes during passive cooling but will act as exhaust vents when you pressurize the attic with the whole house fan.


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