AC blower motor keeps over heating.


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Old 05-27-09, 12:45 PM
J
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AC blower motor keeps over heating.

Hello all. I've been having a problem with my 4 year old furnace/ac unit. The blower motor has been over heating and keeps shutting down.

When we first fired up the ac this year, the condensate drain was clogged and allowed water to run down all over the lower half of the updraft furnace. This wasn't the first time this had happened, so in thinking that the motor was spent, I replaced the blower motor and capacitor. The motor continued to heat up and shut down. I checked the voltage going to the high speed wire and it was reading 120vac and there was no current drawn through the wires. When the unit would cool down and restart, I checked the current and it was reading 7 amps.

To further investigate, I opened up the filter box and tested the system running with it opened up (to eliminate return line problems). The blower still shut down. I then pulled apart the evaporator coil and cleaned it all out (wasn't too bad) and then restarted the system with the A-frame access panel off and the filter box open. The blower still went into thermal protection.

I don't know what to check. Could the problem be freon level/charge related? The blower shuts down after only 5 to 10 minutes, so I'm not sure that the coil has time to freeze up. With the access panel off, I can't see any ice although there is a lot of condensate. I was also wondering if I could be having troubles with the neutral or hot supply on the control board.

Any help would be greatly appreciated! Thanks.

Quick update: I connected the medium speed wire from the motor to the cool terminal and the motor has been running for 15 minutes. Why wouldn't high speed work...
 
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Old 05-27-09, 03:22 PM
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the motor is drawing 7 amps, what is the amp rating on the nameplate? What is the horsepower rating old vs new?
 
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Old 05-27-09, 03:43 PM
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Maybe you do not have the correct motor there, or maybe you have it miswired.

Please post the MFR name as well as the M/N of this furnace

7A sounds a bit on the high side, but as ddjohn says, there's no way to tell for sure without additional information from you.
 
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Old 05-27-09, 07:47 PM
J
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thanks for the replies...

the original motor was pulling around 7 amps (maybe 7.4 i can't remember and it's been pulled out so can't back check).

Furnace
OEM: Trane
Model: CUB100A948C4

Motor
Old: GE, 1/2 HP, 4 spd, 115vac, 1075 rpm (high)
New: Dayton Elec, 1/2 HP, 3 spd, 1075 rpm (high)

I just checked the amperage of the new motor and it is pulling 8.0 Amps. The motor specs show 8.6 full load amps. Here are the specs of the new motor.

Motors > HVAC Motors > Direct Drive Blower Motors > Motor,1/2hp,D/D Blower : Grainger Industrial Supply.

About the wiring... Maybe that was the problem... Turns out that I had connected the blue (medium speed wire) to the EAC terminal on the board. I'm not sure what that is, but it had 119 vac on it. I've since disconnected the blue wire (dangling) and the motor has been running for 15 minutes without a problem. I'll give it the day and post back with the results.
 
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Old 05-27-09, 08:57 PM
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7 amps for a .5 HP motor is fine. Did you make sure you had the right capacitor? Did you check the capacitor?

BTW the EAC terminal is for Electronic Air Cleaner. Its becomes energized whenever the Indoor blower comes on, thus energizing the EAC (if installed). So basically you were sending 120v to 2 legs of the fan motor. This is why you call professionals to do this sort of stuff.
 
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Old 05-31-09, 08:33 PM
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All has been good since making all of the changes. I never checked the original capacitor since the new motor came with its own which was a 370v, 5mfd. After a couple days of successful a/c, i swapped in my original 10mfd cap. the motor starts faster and runs quieter with it. should i go ahead and buy a new 10mfd cap for the system or am i ok to keep my original? by the way, how do you typically test these caps?
 
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Old 05-31-09, 11:29 PM
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You need to put back in the capacitor that came with the motor. There are various tests. Using an analog meter, you discharge the capacitor, place the meter on a 10,000 ohm scale. Touch one meter lead to a terminal on the capacitor and the other to the can. If you get a reading, the capacitor is grounded. Next, touch one meter lead to one terminal on the capacitor and the other meter lead to the other terminal. If the meter needle swings all the way over and stays there, the capacitor is shorted. If the needle does not move, the capacitor is open. If the needle swings over then slowly swings back, that indicates that the capacitor will take a charge, However, it does not tell you anything about the MFD capability of a capacitor. Often, a capacitor is weak and not capable of it's rated capacity. To check that, you need a meter that has a capacitor MFD testing function. One last thing, discharge the capacitor in between each test.
 
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Old 06-01-09, 03:51 AM
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Originally Posted by jryan15
All has been good since making all of the changes. I never checked the original capacitor since the new motor came with its own which was a 370v, 5mfd. After a couple days of successful a/c, i swapped in my original 10mfd cap. the motor starts faster and runs quieter with it. should i go ahead and buy a new 10mfd cap for the system or am i ok to keep my original? by the way, how do you typically test these caps?
Ryan: NO GOOD to swap the "original" capacitor that comes with a motor with one having a different rating. It may do nothing to it, but it may also may affect performance (use more watts), may overheat, and may burn-out. With all these "may" I just mentioned, it is better not to take the risk.
 
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Old 06-01-09, 11:15 AM
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I have to agree. The manufacturer has done extensive testing on that motor design and determined that a 5 uf capacitor is the correct value. You effectively doubled that design value and will likely damage the start winding over time.

While it's true the motor may start faster (because of higher amps through the start winding), you are doing more harm than good.
 
 

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