Single phase condenser motor running backwards

**killer v** · 07-22-2011, 10:46 PM

Forgive my lack of detail as I'm not the one working on the system (and am a new apprentice)...

The basic situation is that we have a single phase condenser fan rotating backwards. The fan blade has not been changed or flipped. The wiring was moved to the other fans for troubleshooting and the problem transfers to the other fans each time. The capacitors have been replaced as well. The problem remains.

It's a Carrier package unit with two stages and three condenser fans.

I understand how this could happen in 3 phase, but what might cause this to happen in single phase?

**Joe Harper** · 07-22-2011, 11:37 PM

Your fan motor has 3 wires just like the compressor (single phase). If the run and start wires are reversed on the capacitor then the rotation will be reversed.

**sfjim** · 07-23-2011, 12:20 AM

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**timebuilder** · 07-23-2011, 07:53 AM

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**killer v** · 07-23-2011, 03:41 PM

Further info:

motor is 460, single phase.

The tech today tried reversing the start and run wires on the capacitor with no change in rotation. He once again moved the wires to another fan and this time, the problem did NOT move with the wires.

I am beginning to think there is a gremlin in the machine.

**hvacjamie** · 07-23-2011, 05:05 PM

the fan may not have the right power at all, and may only be giving the illusion of running backwards. think about this, and see how you could prove that this statement does not apply.

**Rootytootie** · 07-23-2011, 06:27 PM

I have had this problem 2 times so far. Not saying that your answer will match mine cause it may not. So you should check into it more. I found that the motor was bad and the winding was so burned out that it made the motor spin the opposite direction. Everything was wired up right I went over it 3 times. I replaced the condenser motor and wired it the same way and it spun the right way after install. Again not giving you the answer this was just my situation only.

**killer v** · 07-23-2011, 06:53 PM

Originally Posted by hvacjamie

the fan may not have the right power at all, and may only be giving the illusion of running backwards. think about this, and see how you could prove that this statement does not apply.

Well, as I said, I'm a new apprentice...you lost me at "giving the illusion of running backwards." It's definitely running backwards...sucking air instead of blowing.

Are you trying to say that if the motor is under-voltage, it'll run backwards?

**hvacjamie** · 07-23-2011, 07:36 PM

Originally Posted by killer v

Well, as I said, I'm a new apprentice...you lost me at "giving the illusion of running backwards." It's definitely running backwards...sucking air instead of blowing.

Are you trying to say that if the motor is under-voltage, it'll run backwards?

sometimes, if both fans are running, and only one has power, it will pull the other and make it appear as though it is going backwards. other than that, your problem will be in the wiring. study the schematic carefully.

**skippedover** · 07-23-2011, 08:38 PM

Originally Posted by killer v

Well, as I said, I'm a new apprentice...you lost me at "giving the illusion of running backwards." It's definitely running backwards...sucking air instead of blowing.

Are you trying to say that if the motor is under-voltage, it'll run backwards?

Carry on lad. There's a wealth of discussion on this very topic on the pro side. Get your posts up and then apply for pro status. You'll be amazed at the help and discussions and the huge talent pool of those on that side. The motor should not run backwards. If it does, well.....

**killer v** · 07-23-2011, 11:25 PM

Originally Posted by hvacjamie

sometimes, if both fans are running, and only one has power, it will pull the other and make it appear as though it is going backwards. other than that, your problem will be in the wiring. study the schematic carefully.

Now I see what you were saying. The motor is definitely running backwards though. The one time I was there, we isolated it and I gave it a spin in the correct direction. My partner pushed in the contact and it spun back the other way.

Granted, my electrical knowledge isn't quite there yet (more classes coming) but I just can't wrap my head around this one.

**chuckcrj** · 07-23-2011, 11:52 PM

If you're double certain its wired correctly and has a good run cap, throw a new motor in and be done with it.

**Rootytootie** · 07-24-2011, 06:08 AM

I agree with chuck. New one.!

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