Condensor fan will only start with a bump, either direction

Problems related to residential installations.

Condensor fan will only start with a bump, either direction

Postby drdave » Sat May 21, 2011 9:38 am

This is a very old unit, but I'm trying to help out a friend. The compressor turns on but the fan won't start without a bump. The fan will run in the direction that it is bumped, which makes no sense to me. When there is no power applied the fan spins freely in both directions.

I replaced the run capacitor but the problem didn't change at all. The cap I removed was a 6µF, and nobody that I talked to ever seemed to have seen or heard of a 6µF cap. My replacement choices were a 5, 7.5, or 10µF. I chose the 7.5.

I have the skills and tools to fix this, I just lack the knowledge. I don't want to throw my friends money at the wrong items as they can't really afford this. I really thought that the run cap would have fixed this, but it didn't. I really don't want to purchase a new motor, which will be significantly more expensive than the run cap was, if it doesn't resolve the problem.

When you bump the fan and it starts spinning, the unit cools very well.

Any help with this would be greatly appreciated.

- I'm really curious why or how the fan will run in either direction.
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- Condensor fan will only start with a bump, either direct

Postby 4ftBanger » Sat May 21, 2011 10:55 am

A PSC fan motor doesn't really care what direction it spins. It is the job of the start windings of the motor to get it spinning in the right direction, then the reversal of the magnetic poles of the windings act as a push-pull on the stator (rotating magnet) to keep it running. If you have replaced the capacitor (and you are sure the new one is good... I've had more than one that was bad right out of the box) then the motor likely had an open circuit in the start windings. This could be a bad thermal protection device or a broken winding. Not very common but certainly not unheard of. I'd replace the fan motor.
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- Condensor fan will only start with a bump, either direct

Postby drdave » Sat May 21, 2011 11:16 am

Thanks for the reply. You know, I never did test the new cap. It was brand new in the box from a major supplier so it didn't even cross my mind to test it. There are two wires that go to the cap. Is it important which wire of the fan go where? I don't believe so, but thought it was worth asking.

The fan is clearly very old. Looking at it from the top of the unit, the fan wires look really bad, like the insulation is all cracked and brittle.

Since there was not a 6µF cap anywhere, was the better choice to go with the 7.5, or should I have erred on the side of caution and gone with the 5? Since I have to replace the fan motor it's sort of a moot point.
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- Condensor fan will only start with a bump, either direct

Postby 4ftBanger » Sat May 21, 2011 3:19 pm

OK... I've tried to sort this out to make it make sense...

If the capacitor has a wire connected to one of the power lugs - like the top of the contactor - then it has a defined common side and the brown & white wire from the fan should be on that side. Same goes for dual capacitors - the brown & white wire should go to the C terminal. The plain brown wire should almost always be on a capacitor terminal all by itself.

If the capacitor only has two wires connected, and both are from the fan motor, then it doesn't matter which side is which.

I've seen 6uf capacitors before (in fact I have one on my truck right now) I've also got a 2.5uf and a 3uf along with the more common 5, 7.5 etc - That said... the tolerance for capacitors is +- 10%, so is the tolerance on the motor. Anything outside of this range will make the motor less efficient, run hotter, and shorten the motor life... It won't instantly explode or anything like that - I've seen condenser motors rated at 7.5 run with a 10 for a couple years with no detectable issues.
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- Condensor fan will only start with a bump, either direct

Postby drdave » Sat May 21, 2011 8:35 pm

Thanks Matt, it all makes sense. I'll go and get a new motor, and hopefully have it matched with my new cap.

I very much appreciate you taking your your time to help me and to freely share your knowledge with me.
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- Condensor fan will only start with a bump, either direct

Postby kathy » Sun Aug 07, 2011 12:29 pm

The motor I have bought recently works alright
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- Condensor fan will only start with a bump, either direct

Postby Freon » Sun Aug 07, 2011 1:02 pm

When you remove the old fan motor, smell it. If there's the smell of burnt rubber or paper then most likely you need a new motor. However the symptoms you describe are classic for a bad run capacitor. If the windings were going you'd not expect any spinning even after the push. On your way to pick up a new motor, you might stop and have the old motor tested by an electric motor repair shop. It's easy and very inexpensive.
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- Condensor fan will only start with a bump, either direct

Postby heatseeker » Mon Aug 08, 2011 2:07 pm

I would imagine the smell test would work in som e situations but I would not depend on it.
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- Condensor fan will only start with a bump, either direct

Postby nomadpeo » Thu Aug 11, 2011 7:37 am

4ftbanger - thanks for that refresher - i remember the days when there were marks on capacitors to indicate the power side.
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