Sudden loud noise from air handler

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  #1  
Old 05-20-04, 03:27 PM
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dude
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Sudden loud noise from air handler

I now have serious noise and vibration coming from the air handler. It appears to be the blower fan or maybe the motor, but I'm not sure what happened. I can rotate the fan by hand and it turns easily and straight. Same with the shaft on the motor. In other words, I don't think it's a bearing issue. The motor shaft does not seem to have any significant side-to-side movement.

Any ideas on what the specific problem may be?

Thanks,

j
 
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  #2  
Old 05-20-04, 04:43 PM
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Wink

Just a shot in the dark here. if there is not a thing in the blower wheel on both sides. The other thing is that all blower wheels are balanced,Like a tire.They do have weights on them. You might look and see if the blower lost one and that made the noise. They are on the blades if you have some. Look for a spot of no paint on a blade.


ED
 
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Old 05-20-04, 04:56 PM
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Something else to check. The blower wheel has 2 sides. You can see the side that the motor is on by looking in, but if a piece of insulation or something got stuck in the other side, it will change the dynamic balance and not be noticable when you spin it by hand.

Ken
 
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Old 05-20-04, 05:27 PM
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thanks

I guess I'll have to take some things apart and have a look. The vibration when the fan runs is pretty SEVERE, shaking the entire furnace and attached ductwork. It could be a balance issue with the fan- I'll try to take it apart and see- but if so it went way out of balance in a hurry...

Thanks again.
 
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Old 05-20-04, 06:20 PM
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I took the blower wheel housing out

There are three balancing weights which appear to be intact.

A couple of things, though:

1) The wheel rotation appears to be slightly eccentric

2) I found a screw in the housing. For the life of me, I can't find where it came from. It is the same size as the screws that secure the motor support legs, and the legs to the housing, but there are the same number of screws in each of the three support legs (none appear to be missing).

My thought would be to loosen the screws on the motor mount and see if I can adjust the motor to eliminate the eccentricity (radial runout?). It seems logical to me, but the noise and vibration occurred suddenly, the current screws appear secure. Am I barking up the wrong tree?
 
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Old 05-21-04, 05:08 AM
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That sounds odd. If it is out of balance as far as you say, Either something changed the weighting (static or dynamic) or something bent the wheel. There is nothing that could bend the wheel in the airstream though. It might be a good idea to get a new blower wheel. Especially if you are going to do it yourself. All you need to know is direction of rotation (looking at it from the set screw side), width, diameter, and shaft bore size (usually 1/2"). Then you know you are starting with a balanced wheel. If you can't feel any bearing play in the motor, don't bother changing it. The blower wheel has much more to do with the smoothness of running (balance) than the motor does.

Ken
 
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Old 05-21-04, 06:17 AM
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Thanks again

The housing around the wheel appears to be spot welded (?) together so that I don't think I can remove the wheel from the housing. I guess I'll have to get a wheel/housing combo, unless there's a trick to it that I can't figure out.
 
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Old 05-21-04, 07:01 AM
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Look around at that housing for the blower It will all come out as a unit. Look for screws that hold the housing. Sometimes two screws and the whole blower will like slide out housing and all. Turn power off and pull the motor wires ,mark down how they are. You can run it out side just make the motor hot and see what you find this way.


ED
 
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Old 05-21-04, 07:53 AM
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The blower wheel comes out through the air discharge opening. There may be a baffle that needs to removed but once you have the motor off, the wheel should roll right out.

Ken
 
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Old 05-21-04, 04:43 PM
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Doh!

Should have realized the screws on the side would allow the baffle on the housing to move so the wheel could come out.

Upon inspection, it appears to me that the plates that extend between the motor shaft and the fan blades in the center of the wheel have worn the grooves in the blades (where they connect to the plates) radially outward to the point where the plates can shift to one side, making for an eccentric rotation. Also, the plates can easily rotate without moving the fan blades when set on end. Please let me know if there's some trick of the trade to make sure these plates stay centered.

Anyway, I was 99.99% sure this must be the problem, so I tried to buy a new wheel, but no one around here that had one would sell me one. I did find one place that can get one for me on Monday...
 
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Old 05-21-04, 04:59 PM
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Get the new one. There should be nothing that moves on that whole assembly. Something must have worn or come loose. It shouldn't be too expensive and it will return to normal after that. Be glad it didn't take the bearings out of the motor.

Ken
 
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Old 05-22-04, 04:55 PM
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Could try Grainger or Johnstone supply and see if they will sell to you .

ED
 
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