# Carrier a/c condenser fan motor still running slowly after thermostat is satisfied



## GetYourShineBox (Sep 20, 2009)

i was checking out a unit today in the complex i work at and after the thermostat satisfies the condenser fan motor continues to run but at a much slower speed and hums loudly. the only way to kill the power to it is pull the disconnect or flip the breaker. the contactor operation checks out ok. the capacitor checks out ok. the ohm readings for the fan motor seemed off. my conclusion was that the fan motor is faulty. any ideas?


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## yuri (Nov 29, 2008)

Read this post CAREFULLY especially my answer at #9. You may have a shorting compressor and it can be VERY dangerous or deadly.
http://www.diychatroom.com/f17/plea...ompressor-fan-hissing-noise-compressor-74783/

If it is a single pole contactor (bridged across one side) the compressor and motor can be powered up thru the short in the compressor.


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## GetYourShineBox (Sep 20, 2009)

yuri said:


> Read this post CAREFULLY especially my answer at #9. You may have a shorting compressor and it can be VERY dangerous or deadly.
> http://www.diychatroom.com/f17/plea...ompressor-fan-hissing-noise-compressor-74783/
> 
> If it is a single pole contactor (bridged across one side) the compressor and motor can be powered up thru the short in the compressor.


the compressor seems fine. its not running or making any sounds when the thermostat satisfies. just the fan motor hums and runs slowly. but when i turn the power back on to the unit without hitting the thermostat the motor just hums and the blades do not turn. its when i hit the thermostat and then turn it off that the fan blades will turn at a slow speed. i just want to make sure what the problem is before i give false information. its only my first year in the field.


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## yuri (Nov 29, 2008)

It should not hum and as the compressor shorts out worse it will get worse. You need to disconnect power to the unit. Then remove the 3 wires to the compressor. Then use an ohmeter and check each terminal to the copper suction line of the compressor. If you get any continuity then the compressor is shorting. Do you have any Journeyman techs at your company. If so ask them politely for some advice or to go there with you and show you how. Don't be afraid to ask for help. We all started somewhere. The Boss may give you credit for being conscientious. Thats what I look for in my apprentices.


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## GetYourShineBox (Sep 20, 2009)

yuri said:


> It should not hum and as the compressor shorts out worse it will get worse. You need to disconnect power to the unit. Then remove the 3 wires to the compressor. Then use an ohmeter and check each terminal to the copper suction line of the compressor. If you get any continuity then the compressor is shorting.


ok i will try that. but what if that isnt the problem?


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## yuri (Nov 29, 2008)

Reread my post I added to it. It should not hum. If it is not the compressor then there may a short in the wiring or a bad capacitor or sticking contacts in the contactor. Cannot see it from here unfortunately. I go out on jobs to help my apprentices with odd situations like this. Better to ask a question than to ignore a problem and prove your ignorance later is what I tell them.


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## GetYourShineBox (Sep 20, 2009)

ok i will double check it tomorrow and post results. and no i left the hvac company i was working for certain reasons and now i am doing property maintenance. i am the only epa certified guy there and overall the only one with any schooling for it.


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## yuri (Nov 29, 2008)

DO NOT touch the compressor while this is happening!! You will become the circuit to ground and may get electrocuted!


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## GetYourShineBox (Sep 20, 2009)

ok so i did the compressor terminal check and i didnt get any continuity. i double checked ohms for compressor and for the fan motor. for the compressor i got. black and yellow = 6.9 . blue and black = 10 . blue and yellow = 10. fan motor ... black and yellow = jumping around between 1 and 2. brown and yellow = jumping around between 1 and 2. and brown and black = 60 ohms. also i recorded a video of what it is doing. 

http://www.youtube.com/watch?v=zGjbw5bAIO8


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## yuri (Nov 29, 2008)

Very strange. Hang in there for a couple days so more Pro's see it and may help out. I PMed you with a Pro site to try.


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## Marty S. (Oct 31, 2009)

You have a short to ground somewhere. Check each and every lead from the contactor and you'll find it. Not blowing the breaker because it's going through a load before getting to ground so has to be motor windings or compressor windings.


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## mikethe ductman (Jun 2, 2010)

Had a Ruud 2 ton H/P do the same thing today.

I unhooked the two comp. leads to the contactor and the fan still ran, I unhooked the comp. lead to the ran cap. and the fan stopped turning.

I my case the comp. was tripping the breaker

My contactor only broke one leg, with one hot leg and a short the fan will try to start.

Like yuri said be carefull or it might be lights out.


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## beenthere (Oct 11, 2008)

Your compressor ohms are good. Did you have all the wires removed when you checked it?

Does that unit have a start capacitor and relay on it?

Does it have a CCH. Crank Case Heater?

Did you check the capacitor to see if its shorting to ground?

Did Mary really marry John? LOL


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## GetYourShineBox (Sep 20, 2009)

beenthere said:


> Your compressor ohms are good. Did you have all the wires removed when you checked it?
> 
> Does that unit have a start capacitor and relay on it?
> 
> ...


start capacitor. i checked the cap for a ground fault and got nothing. no cch. mary cheated on john. i still think its the fan motor. i just hate being wrong.


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## Marty S. (Oct 31, 2009)

I'm thinking compressor. Common to start 6.9, common to run 10 and run to start 10 ohms. Those don't add up and are more then double any residential compressor I checked. Check another compressor in the complex and see how it compares. In the mean time put contactor on there that both sides open.


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## beenthere (Oct 11, 2008)

That was suppose to say" your compressor ohms AREN'T good".


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## GetYourShineBox (Sep 20, 2009)

yeah if it is the compressor i dont see the unit being changed out anytime soon. i guess for now the tenant will just hit the breaker everytime it shuts the unit off.


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## beenthere (Oct 11, 2008)

If its the compressor. And left go like this for too/much longer. It will end up being a severe acid burn out. And if not cleaned up properly. Will wipe out replacement compressors fairly quickly. And cost a lot more to keep on replacing them every few months/weeks.


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## MEMPHISBIGC (Jun 14, 2013)

beenthere said:


> Your compressor ohms are good. Did you have all the wires removed when you checked it?
> 
> Does that unit have a start capacitor and relay on it?
> 
> ...


Hey, I'm having the same problem with my Sisters A/C. The Condensor Fan runs slowly when contactor is not energized, as if it is running off 1 leg (120)Compressor will not start up. Capacitor check good. When contactor energized (call for cooling), Fan starts up at 240 Fan speed, Compressor will not start up. I was thinking Grounded Comp/ keeps tripping 240 House Breaker. What did you find out in your situation?


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