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Washroom exhaust fan blowing air instead of sucking air

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  • Oct 5th, 2009 2:52 pm
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Jr. Member
Jun 9, 2008
161 posts
8 upvotes

Washroom exhaust fan blowing air instead of sucking air

I replaced the motor in my washroom exhaust fan. I realized now that the fan is blowing air into the washroom instead of exhausting it out like it should. I'm pretty sure the fan is not reversed or anything. Did I reverse the + and - wires to the fan? Is it safe to just flip them back?
7 replies
Deal Fanatic
Mar 21, 2002
5720 posts
508 upvotes
My guess:
This is probably an AC 120 volt motor and as such reversing the wires doesn't change the direction of rotation (that only works with DC motors). AC motors are mechanically designed to spin in either one direction OR the other direction but are not capable of both. You've got the wrong motor - you need one that spins in the opposite direction. If you take the motor out and look at it you should see an arrow on it somewhere showing the only direction of rotation that that motor is capable of.
Deal Guru
User avatar
Jun 12, 2007
10905 posts
1323 upvotes
contextv wrote:
Sep 26th, 2009 7:05 pm
I replaced the motor in my washroom exhaust fan. I realized now that the fan is blowing air into the washroom instead of exhausting it out like it should. I'm pretty sure the fan is not reversed or anything. Did I reverse the + and - wires to the fan? Is it safe to just flip them back?
Can you take the fan blades off the motor and flip them over the other way?
[OP]
Jr. Member
Jun 9, 2008
161 posts
8 upvotes
I don't see how I could've gotten the motor wrong since I bought it as a packaged box from Home depot. Unless I installed the motor upside down?
Deal Fanatic
Nov 13, 2002
5461 posts
100 upvotes
contextv wrote:
Oct 3rd, 2009 11:46 pm
I don't see how I could've gotten the motor wrong since I bought it as a packaged box from Home depot. Unless I installed the motor upside down?
might be a factory error, take it back and ask the guy in home depot to figure it out, make sure to remember in what direction you installed it, put a piece of tape to identify the underside or something...

I bought one of those 40$ Broan ones from HD, and it isn't powerful enough for anything.
Deal Addict
User avatar
Mar 8, 2002
3454 posts
434 upvotes
Ottawa
Due to fan dynamics sometimes if you hold your hand up to the grille, it may seem like air is coming out instead of going in.

Put a piece of paper over the grille while the fan is running as a test.
Member
Feb 17, 2004
423 posts
58 upvotes
If the fan is not turning the wrong way I suspect your exhaust ducting or outdoor vent is blocked. If you plug the vent it's going build pressure and blow back into the home.

Go outside and find the vent. Check that it is closed when fan is off and the flap opens when fan is on.
Deal Fanatic
User avatar
Jan 18, 2004
6544 posts
261 upvotes
Markham
MacGyver wrote:
Oct 4th, 2009 7:26 am
Due to fan dynamics sometimes if you hold your hand up to the grille, it may seem like air is coming out instead of going in.

Put a piece of paper over the grille while the fan is running as a test.
v82slo wrote:
Oct 5th, 2009 2:44 pm
If the fan is not turning the wrong way I suspect your exhaust ducting or outdoor vent is blocked. If you plug the vent it's going build pressure and blow back into the home.

Go outside and find the vent. Check that it is closed when fan is off and the flap opens when fan is on.
+1.

The "fan" is usually a cylinder with curved ridges designed to push air laterally towards the ducting and not actual fan blades like in a ceiling fan that would push the air vertically. So it shouldn't be possible that the fan is spinning backwards and blowing air, but you can clearly see when it spins whether its spinning the correct way (concave forward). Check the vent for blockage as already suggested. You should be able to push the little flap and make sure it opens.
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