Furnace blower motor overheating- using evaporative cooler motor

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  #1  
Old 10-10-18, 09:30 PM
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Furnace blower motor overheating- using evaporative cooler motor

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, 10:37 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, 07:55 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, 08:05 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.
 
  #5  
Old 10-21-18, 08:05 AM
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Replacing furnace blower PSC motor with evaporative cooler motor

hi

As an effort to increase the CFM from my furnace, I am wondering if I can replace the existing 3/4HP 1075 rpm motor with 3/4HP 1725rpm motor which I can get for very cheap price. I am wondering what could be negative with doing this?
 
  #6  
Old 10-21-18, 10:02 AM
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Why do you need to increase the CFM of the furnace? Also I do not know where you will purchase a 1725 rpm motor that will mount as the 1075 RPM motor will. Turning that blower at 1725 RPM would probably move way too much air and overload that 3/4 HP motor. Please explain your thoughts as to why you want to move more air than the present motor/blower combination can move. What are you trying to accomplish? Has something changed in your existing system?
 
  #7  
Old 10-21-18, 11:31 AM
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Combined two threads..............
 
  #8  
Old 10-21-18, 06:50 PM
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Two of the rooms in my houses have constant issue of being hot in summers and cold in winters. When I measured airflow from the ducts I noticed a normal room gets about 200ft/min and these two rooms only get 105ft/min. This is despite of ensuring the duct shutter is fully open and register has the grill with max opening.

Also, I recently added three more ducts in my basement which has worsen the situation.

To stabilize the temperature across all rooms I can partially close the duct shutter in other rooms but that will put more load on the blower. Instead I want to get at least 200ft/min Air flow in the two rooms in order to stabilize the temperature.

I understand by increasing flow it will immediately cause temperature rising it falling but when I come this with intermittent fan running I can over come this issue.
 
  #9  
Old 10-22-18, 09:05 AM
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I'm not an expert, but it seems to me that even if you do increase the fan speed (increased cfm), you'll still have the imbalance issue. The rooms that are currently getting more airflow will get even more and the rooms with reduced airflow likely won't see any improvement in temperature swing. While they may see an increase in airflow, since the other rooms will also get more airflow, the amount of heating/cooling per room will likely stay about the same. I think you need to close the dampers slightly on the rooms that have good airflow to send more of the air to the rooms that are further away. Ideally, this should be done via a damper in the air duct as close to the air handler as possible, rather than closing the damper on the register in the room.
 
  #10  
Old 10-22-18, 10:07 AM
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Ok thanks for the suggestion. I will give it another try again and will if it helps. One thing I am also thinking about is to continuously run the fan with slower fan speed. Maybe this will also help.
 
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