I have a Goodman heat pump and the indoor fan motor (230v, 1/2hp) will kick the overheat about 1 minute after start up. The fan seems to run fine for that first minute. I changed the start-run capacitor and the motor still kicks the overheat after about 1 minute. This is a three wire motor with the capacitor between the brown START wire and the yellow COMMON wire. I measure 19 Ohms between the START wire and the black RUN wire and 13 Ohms between the COMMON wire and the black RUN wire. The fan spins freely by hand and the coils of the motor show no signs of extreme heat though you can feel that the motor is hot when it shuts off. The motor overheats even if the door of the heatpump is left open letting the fan suck all the air it can and there seems to be normal air flow through the duct work.

You ideas are appreciated.

 

Is the capacitor you installed of the correct rating for the motor?

 

Welcome to the forums.

Does the motor start briskly and quietly....... no groans or strange noise ?

 

The capacitor has the identical specs as the original, and both old and new capacitors match what is written on the plate on the motor. We have run this heat pump for 5 years with no problems prior to this.

The motor is quiet and except for getting hot seems to operate normal up to the point the overheat trips out. I find it odd that it doesn't show any other symptoms than the overheating. No noises, no slow starting, no low rpms, etc.

 

Can you test for and confirm +/- 240vAC at the motor ?

 

I have the motor out and apart on the bench and see nothing wrong with it, but will put it back together and give it power while on the bench tomorrow. When it first went bad a month or so back I did check the voltages but was less sure of how the motor was actually wired. Now I am one hundred percent sure that I understand the wiring, though I don't understand what "turns off" the start capacitor once the motor picks up speed as there is no centrifugal switch to do such like I have seen in larger motors. Guess I need to do some more reading on small AC motors.

 

That's a split phase motor. A capacitor acts like a dead short when the motor starts up.

A basic description.....
So on power up.... the run winding is powered and the start winding receives full voltage from the non charged cap. The cap charges in under 1/2 of a second and then the start winding only receives a slight voltage based on cap value. Too high a value will allow to much voltage to get to the start winding during run.

 

Well, the problem became obvious as I began to reassemble the motor and thus gave it a cleaning and more careful inspection. For some reason the rotor has migrated along its shaft about 5/8" from its original position, so the rotor is badly out of alignment with the stator. Can't 100% say if this is cause or effect (or both) of the overheating. From the rust and dirt on the shaft it looks like the movement may have been gradual over time, but whatever it was I can not get the shaft to move back through the rotor, even though I have applied considerable force (a four pound drilling hammer wailing on the end of the shaft via a heavy brass bunch).

I can guess that at some past point the start capacitor went bad and the rotor got burning hot while vibrating back and forth and as a result moved a bit on the shaft and then in subsequent running it would get enough at times move a bit more. Over time it moved enough that the stator too was getting hot and the overload eventually kicked.

Whatever happened I think a new motor is in order at this point in time.

 

I've seen strange motor failures. Even high heat doesn't usually cause the armature to move. It could be press fitted and loctighted. But you're right..... time for a replacement.