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Exhaust Shutter Fan Doesn't Suck

Posted by davey4000 (My Page) on
Fri, Jun 15, 07 at 21:55

I bought a 120V shutter style exhaust fan, installed it, powered it up and it blows in instead of out. Obviously, the shutters just stay closed. How can I reverse the air flow? It seems all I would need to do is loosen the set screw on the collar holding the fan blades to the motor shaft, turn it around and reclamp. Will this work?


Follow-Up Postings:

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RE: Exhaust Shutter Fan Doesn't Suck

Some possible scenarios I could think of:
1. The fan was manufactured incorrectly and was placed facing the wrong direction. This is highly unlikely though.
This would mean that the entire motor itself is backwards, not just the blades. Since you can flip the fan blades any way you want, if the motor rotates the wrong way then the air will be moving in the wrong direction.
I am not sure how the fan made it out of quality control if thats the case.

2. The fan is wired incorrectly so that the motor is rotating in the wrong direction. Not sure of the exact conditions for this to happen, but it can happen.

3. The fan might be a "reversible" or "convertible" fan? Some fans have a switch that allows the fan rotate clockwise or counter clockwise so that the air can be forced in either direction.

You should contact the seller first to see if they have any ideas on whats going on before you attempt to tweak it.


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RE: Exhaust Shutter Fan Doesn't Suck

Take a picture of the whole thing, and take a picture of the motor name plate.

We will be able to tell better what's the problem

dcarch


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RE: Exhaust Shutter Fan Doesn't Suck

Couple of things just came to my mind:

1. Turning the blade will not change the air flow. It will be the same. The only way is to turn the motor around, if it has a shaft on both ends.

2. The fan may be working correctly but the shutters may be stuck. When a fan is block, air flow may be force (bounce) backwards.

Check again.

dcarch


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RE: Exhaust Shutter Fan Doesn't Suck

I reversed the blades and it blows out, toward the shutters, now. I don't particularly like this solution because the position of the locking collar now puts the blades within 1/4" of the cage.

The motor turns counter clockwise. I could reverse the hot and neutral, but I didn't think that made any difference on a 120V AC motor. I do not see a switch to reverse the direction either.

I will post some pictures later. I'm out of town on business for two weeks.

Thanks for the suggestions.


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RE: Exhaust Shutter Fan Doesn't Suck

No. I don't think so. Something is not right here.

It is simple geometry (not logic). Turning the blades backward will give you the same air blowing direction as before.

dcarch


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RE: Exhaust Shutter Fan Doesn't Suck

I think he reversed the entire motor on the mount. Hence the awkward fit of the blades along the cage.


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RE: Exhaust Shutter Fan Doesn't Suck

Doesn't sound like that's what he did. I can't see exhaust fan/shutter assembly would let you turn the blade/motor that way. I guess picture may explain a lot.

dcarch


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RE: Exhaust Shutter Fan Doesn't Suck - Davey

I would have returned it for one that works correctly right out of the box.


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RE: Exhaust Shutter Fan Doesn't Suck

>>I guess picture may explain a lot.
Yeah I am curious as to whats going on here :)


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RE: Exhaust Shutter Fan Doesn't Suck

Posted by dcarch (My Page) on Tue, Jun 19, 07 at 18:48

No. I don't think so. Something is not right here.
It is simple geometry (not logic). Turning the blades backward will give you the same air blowing direction as before.

dcarch


Turning the blade around will make it blow in the opposite direction just like when you reverse a ceiling fan it blows either up or down depending on which way it is turning.


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RE: Exhaust Shutter Fan Doesn't Suck

This would be a good one to win some money :-)

By turning (flipping) the blade around will not change the direction of the air flow.

Changing the direction of the blade rotates will.

dcarch


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RE: Exhaust Shutter Fan Doesn't Suck

>> Turning the blade around will make it blow in the opposite direction just like when you reverse a ceiling fan it blows either up or down depending on which way it is turning.

Huh?
Are you talking about reversing the rotational direction (clockwise vs counter-clockwise)? or just flipping the blades?
Flipping the blades around will still result in the blade angles oriented the same way.
To reverse the airflow, you will need to reverse the rotation of the blades.


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RE: Exhaust Shutter Fan Doesn't Suck

Posted by wetfeet101b
To reverse the airflow, you will need to reverse the rotation of the blades
Yes you are correct you will need to turn the motor in the opposite direction.
Someone earlier had the best idea just send it back and have them send one that works.


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RE: Exhaust Shutter Fan Doesn't Suck

"Someone earlier had the best idea just send it back and have them send one that works."

Not necessarily. The problem may not be the fan.
It is almost impossible for A/C induction motors to be running backwards. Unless it is a universal motor, which is not commonly used, or a DC PM motor which is also not generally used.

dcarch


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RE: Exhaust Shutter Fan Doesn't Suck

Several of you suggested that reversing the fan blades will not change direction of air flow...it does. See my second post. By reversing the fan blades I mean taking the fan blade assembly off the motor shaft, turn it over and put it back on. The motor still runs counter clockwise and the air flow is now reversed, blowing out toward the shutters as it should.

The only problem I see with this solution, if you call it one, is that now the blades are within 1/4" of the cage due to the locking collar now being on the opposite side of the fan blade assembly.


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RE: Exhaust Shutter Fan Doesn't Suck

That's very interesting. May be we are confusing each other.

If the motor rotates in the same direction as before, and you are only taking the fan blade and flipping it front to back in reverse but still rotating in the same direction, then the air flow will still be in the same direction as before you flip the blade.

dcarch

The only way to change air flow is to reverse the rotation of the motor relative to the fan blade.

Posting a picture may clear up your problem.


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RE: Exhaust Shutter Fan Doesn't Suck

Here is another theory:

1. Each "leaf" of the fan blade has a pitch (angle), in addition, each leaf is slightly curved. Although it operates either way, front or back, one way blows lots more air than the other, (in the same direction).

2. If the blade is installed the wrong way, there is not enough air pressure to push the shutters open, but the air is bounced back as if the fan is blowing the wrong way.

3. So when you flip the blade around, the air pressure is now strong enough to push the shutters open. When you said that you flipped the blade and the blade is now closer to the cage, that's what gave me the clue. The set screw that secures the blade to the motor shaft should put the blade closer to the cage. 1/4" from the cage is not a problem if that makes the fan work. May be this is the correct way.

dcarch


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RE: Exhaust Shutter Fan Doesn't Suck

Another way to visualise the effect of flipping the blades only is to look at a screw. It has a right hand thread no matter which way it is oriented. Turn it clockwise and it advances forward. Flip it and turn it clockwise and it still advances forward.


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RE: Exhaust Shutter Fan Doesn't Suck

Here are photos of the exhaust fan. I've never used Photobucket before. I hope this link works.

http://s182.photobucket.com/albums/x293/davey4000/


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RE: Exhaust Shutter Fan Doesn't Suck

Interesting.

Based on the pictures, yes, you have installed the blade backwards (the setscrew should be the other way on the motor shaft normally).

Fan blade leaves have "pitch" (angle) in order to push or pull air, in addition, each leaf has a curve (concave or convex) depending if the fan is to push or pull. The picture seems to show the curve of the blade leaves are designed for pulling of air. So when you flip the blade, (as shown on the pictures) and the motor is rotating CCW, the air is being pushed efficiently out. Before you flip the blade, the air was still being pushed out, except the push was very inefficient because the curve was the wrong way.

It appears that the blade is made for a fan intended for pulling air for a motor running CW, as in airplane engine, which is not very common.

Its possible that in the factory things got mixed up.

dcarch


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RE: Exhaust Shutter Fan Doesn't Suck

Did the cage and shutter come with the fan kit that you bought?
That looks like a "Whole House Fan" setup to me.
Those fans are meant to be set up on the ceiling and suck the air up into the attic or vents. The motor will be on the "downwind" side of the fan.

Here is a link that might be useful: Whole House Fan setup


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RE: Exhaust Shutter Fan Doesn't Suck

dcarch & wetfeet: Thanks for the comments. I have two fans. I have not touched the blades of the one pictured yet. It blows inward, not toward the shutters as it should. I have reversed the blades of the other fan (not pictured) and it now blows toward the shutters.

The fans came from Greenhouse Mega Store and is designed specifically for greenhouses. Their URL is http://www.greenhousemegastore.com/Home.asp. The fan, cage and shutters came assembled right out of the box in one piece. They are not whole house fans. They measure about 16" x 16". The manufacturer is JD Manufacturing. I spoke with them and they are supposed to check something (?) and call me back. I have not heard back yet and it's been 4-5 days.

Oh well, I'll reverse the blades on the other fan and start using them. It seems to work ok that way.


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RE: Exhaust Shutter Fan Doesn't Suck

Let's look at it this way. If the fan was pulling air in the wrong direction and not blowing against the slats, something was wrong with the way it was built. Take the fan out. Buy a couple of box fans for temporary ventilation and return your fan to the store. They should correct the problem.


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RE: Exhaust Shutter Fan Doesn't Suck

I agree. The fans are not working properly, and they should take care of the problem promptly. Please keep us informed of your progress.


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RE: Exhaust Shutter Fan Doesn't Suck

I have one of those, still in the box (!). The one you've pictured has it's blade on backwards. Except that yours is (are already both?) installed, as you've probably found out it's a trivial matter to take it apart & change it.

Some kid in the factory assembled yours wrong. Unless the shutters are bent or something I certainly wouldn't go to the bother of returning them--just flip 'em around.

But I am a little suspicious of the 1/4" clearance you cited--mine has plenty more all-around than that. I wonder if that kid put a larger blade assembly on yours by mistake. But it shouldn't be a problem unless it touches the cage... I'd consider it a bonus for my trouble!!!


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