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Help: Carrier Condenser Fan Humming - Capacitor and Contactor already replaced

Air Conditioning and Cooling Systems - DoItYourself.com Community Forums - www.doityourself.com
My Experience Level:

Hi. I just thought I would first mention that I have done this repair to 3 or 4 units at other homes I have lived in successfully. I am not an HVAC trained tech but I am very comfortable working with the equipment.

So, here is the situation and what I have tried already. I will try to be as detailed as possible in this one first post but it will be a bit lengthy. I will also give updates with any additional info if needed. Can anyone help?

Initial Problem:

My Carrier condenser fan suddenly stopped working yesterday. Usual symptoms of a bad dual run capacitor was my first guess so I ran out and checked the capacitor with an ohm meter and the HERM terminal tested fine but the FAN terminal tested bad. So, I ran out and bought an exact replacement dual run capacitor 440VAC 70uf /7.5uf and replaced it. Yes it is definitely wired correctly

I restarted the system (set thermostat 1 degree below inside temp) and it worked perfectly fine and the fan kicked on beautifully and worked with no humming! When the house dropped by 1 degree the fan and compressor tripped off perfectly fine as expected.

WEIRD PROBLEM:

When the house went back up 1 degree inside and the thermostat kicked on the second time then the problem returned with a humming fan not spinning on the condenser! The compressor kicked on fine but the condenser fan stayed there humming away and trying to turn very slowly. I tried spinning the fan blades with a stick to get it started and that could not get it to spin. I checked the ohms on the new capacitor and it seems fine.

What I noticed:

If I leave the system off for about half hour and then started it back up again then the fan kicks on perfectly fine again but when it goes off after cooling the house and it tries to restart again after the temp raises inside then the fan doesn't start the second time and just humms and does not spin.

Next replacement part is the 24VAC contactor:

So, I ran out and bought a new contactor and replaced it also as I thought it might be that. Even with a new capacitor and a new contactor still the exact behavior as described above and yes everything is wired perfectly right (checked it 10 times).

Next on to the Fan Motor:

So I thought the next step would be to test the actual motor before running out and buying a replacement. I tested the wires on the motor for ohms and everything checks out fine. I used the usual test to check ohms between each wire (yellow and ground and then Brown and ground) and then add them up and see if they are the same as the ohms on the two non-ground wires (brown and yellow) to see if they match. Everything adds up and that would PROBABLY suggest that the motor is also good.

Questions:

What else can I check other than running out and buying the fan motor and replacing it??

I am willing to go buy the motor and replace it for $200 but what if I end up with a replaced motor and a replaced dual run capacitor and a replaced contactor but still have the same issue?

Is there anything else to check that I am missing? I am 100% certain everything is wired correctly and also I have cleaned all wire ends and connected them tightly.

I will be happy to provide any other info or try other tests that anyone else suggests before running out and buying a new fan motor.

Could it be possible that the fan motor IS bad and it only works sometimes and not other times or is it usually that if the motor is bad that it just flat out won't work at all?

Thanks! (Phew that was a lot of typing)


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