New furnace blower motor overheating

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  #1  
Old 10-10-18, 08:30 PM
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New furnace blower motor overheating

Hi

I want to increase the air flow from my furnace while the original motor is running fine at its speed of 1075 rpm, 3/4HP. I bought 1HP 1625 RPM motor (model US Motors 1699) thinking that it will increase he CFM output of the blower. Shockingly the motor is running much slower than the current motor and also it's getting over heated. This motor came with new capacitor 25MFD 370v. I also tried another new motor 1/2HP 1625RPM with new 15mfd 370v capacitor...same disappointing result.

I just fail to understand why are the new motors running slower than the old motor. When I put the old motor back it runs like a charm.

Both the new motors are bi directional and the original one is CW directuonal.

Can any one please suggest me what's going wrong here? I am connecting all wiring per instructions like white being common and black being fastest speed. Two brown wires for capacitor.

When I run both new motors without installing them, basically without the blower wheel, they run fine at high speed with no overheating. Both new motors have long shaft than the original motor....

I have good technical understanding of things but this situation is really driving me crazy. Can someone please help me?

Thanks
 
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  #2  
Old 10-10-18, 09:37 PM
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This problem is probably caused by the higher external static pressure created by your new motor. Since it is unlikely that you also increased the ductwork I can see this becoming an issue.

1 HP 1075 motor would have given you more air.

It looks like the new motor is a 115 volt single speed motor?

Most 115 volt blower motors that I see are 3 speed.
 
  #3  
Old 10-11-18, 06:55 AM
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Update:
Hi. Both new motors I tried are three speed. The original motor is 5 speed but only two speeds are used by the control unit. I thought it would be simple...higher rpm with more HP should work solid.

Seems like my current motor is already running at 1075rpm then not sure if there will be any change in CFM after putting 1HP1075rpm.

I tried running the blower outside the furnace with both new motors and I see the same behavior. As soon as I put the blower wheel on the new motors I see they can't bear the load and run slow with getting overheated. I also noticed that the 1HP 1625RPM motor was taking over 1600Watts, without blower wheel on, it consumes around 200watts. The current motor performs the same with the blower wheel outside the furnace as well inside with 900 watts consumed (3/4HP 1075 rpm). I haven't tried to put the blower inside the furnace with new motors as they already get overheated outside and I don't want to burn wiring or the circuit board, at least it's fuse.

Another thing I noticed that when I change direction of the motors to run CCW with blower wheel on, they run very fast, but obviously no air output from blower since it's wrong direction.

Is there anything I should try with both the new motors? Both motors came with new sealed capacitors.
 
  #4  
Old 10-11-18, 07:05 PM
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By static pressure....... it's not like static when you get a shock. It's the pressure the system puts against the blower. There are a lot of factors that go into selecting a motor size.
 
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