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#25579 - 05/13/03 11:49 AM Air condenser motor??
sparkync Offline
Member

Registered: 10/17/02
Posts: 811
Loc: NC
Anybody out there know any details about central air conditioning unit?? One of my electrical customers called me and has a central a/c unit that started squealing and making noise and she said it got real hot. When I got there the condenser fan would not run when the compressor came on. The motor is not locked up. I checked the voltage from one side of the contactor to one side of the capacitor that goes to the motor and was getting around 350 volts. I assume that is normal since that is what the capacitor is for to help start the motor. Is there anything else that could cause the fan not to run in this situation. I'm just trying to remove all doubts before I order this motor for her. Thanks for any input.. Steve....

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#25580 - 05/13/03 02:44 PM Re: Air condenser motor??
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
You might check or replace the oval/metal-can run capacitor first. It is possible to tell if the cap is not completely open or shorted with an ohmmmeter.

Remember that most "39-frame" appliance motors have internal thermal cutouts that will often reset after cooling. Electrically, the motor sill run but draw over nameplate current until the cutout opens.

Not 100%, but worn sleeve bearings tearing up the motor shaft are a major cause of failure—and not worth trying to repair.

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#25581 - 05/13/03 02:49 PM Re: Air condenser motor??
maintenanceguy Offline
Member

Registered: 12/02/01
Posts: 303
Loc: Southern NJ, USA
Lots of different setups for AC.

The condenser fan may be on a pressure stat and automatically turns on and off to maintain a specific pressure in the condenser coil. On a cool day it would be off more than on. Called a low ambient control. A freon leak or undercharge can also cause this.

If it's a bad cap, you can of course test the cap but if you don't have a cap feature on your meter, give the condenser motor a spin by hand. Because the capacitor is only used for the start winding, a motor with a bad capacitor will run fine if you start it by hand. One of the symptoms of a bad capacitor is a fan motor that is found running backwards, without a start winding to start it the right way, it will run in either direction.

And of course you can ohm out the motor to check for open windings or a short to ground.

If the bearings on the condenser fan don't squeal, she might have hear the compressor short cycling. Scroll compressors can usually start pretty well under pressure but some compressors need a few minutes for the freon pressures to equalize or they can't get going and can make some odd noises. Adding a delay on break (DOB) or delay on make (DOM) timer can help prevent short cycling which can be caused by all sorts of things.

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#25582 - 05/13/03 04:37 PM Re: Air condenser motor??
frank Offline
Member

Registered: 05/29/01
Posts: 361
Loc: windsor ontario canada
thermals are probably shot.does it start if you give it a spin? if so check cap only cost 10 bucks to replace?

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#25583 - 05/14/03 01:43 AM Re: Air condenser motor??
zapped208 Offline
Member

Registered: 02/18/03
Posts: 201
Loc: Somewhere in USA
nc,- best advice is have your customer call their HVAC contractor.
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