AC compressor starts, but fan does not turn


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Old 07-20-08, 05:45 PM
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AC compressor starts, but fan does not turn

Hi Guys,

I came across your forum while trying to figure out what is wrong with my AC. As the subject states, the compressor starts, but the fan does not spin. I took the air conditioner apart today and verified that the fan does spin if you do it manually, so I know it is not a bearing.

From the research I have done it sounds like there are two common things. The first one is a bad capacitor, the second being a bad fuse. I pulled the fuse out of the box on the house and looked it. From what I can tell, everything looks fine, but I guess I am not sure how they are supposed to look. How can you tell if a fuse is still good.

I have also read that there is way to test the capacitors with a multimeter. I have a multimeter, but am not sure how to test the capacitors. Can anyone give some insight to this? Also, are they safe to disconnect, now that I have the fuse unplugged?

I have included some pictures of my AC unit. Please let me know if a picture of something else would be helpful.

Thanks

Dave







The fuse:

 
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Old 07-20-08, 07:48 PM
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First question I have for you is: which fan is the one that is not spinning? Is it the fan that is on top of the compressor (in the outdoor unit), or is it the fan inside the furnace (the one that moves air via the registers throughout the house)?

Second question: I can't make sense of the first picture. The other three show the capacitors and contactor, all of which inside the unit outdoors.

The black capacitor is called a "start cap". It is obviously good since the compressor (as per your posting) is starting and running o.k.
The silver capacitor is called a "run cap". From the picture at least, it shows no bulging, so it appears (visually at least) that it's o.k. too. Which brings my first question on the table again: which fan is the one that is not running?

To test capacitors you need a multimeter that is "capable" to test/read capacitance. If it does not have that feature then is not useful for your purposes.

How do you know you have a bad fuse? Make sure the power is not disconnected and with the multimeter set to read volts, check the voltage. It should read 220V inside the fuse box by the outdoor unit...but the compressor IS running, so lack of power is "not" your problem.
 
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Old 07-20-08, 09:41 PM
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Hi Pflor,

Thanks for your response. The fan that I am talking about is the one that is outside connected to the air conditioning unit. The indoor fan is working just fine. The first picture is just another angle of the silver capacitor.

I am not sure if my multimeter can test/read capacitance, but it doesn't look like it. Here is a link to the one I have. http://www.amazon.com/Craftsman-8208.../dp/B0007ICQI4

If this multimeter is not capable of what I need, would there be a place I could take the "run cap" to get it tested? I'm still hesitant to touch it, since I know capacitors can still hold a charge after the power is been shut off. Is it safe to touch the "run cap" to disconnect it/test for bulging?

Thank you for your help.

Dave
 
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Old 07-21-08, 12:57 PM
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The meter you have can't test capacitance.

Where can you take the cap to be tested? Try your luck at your local Graingers Supply.

You have two caps there. The black one is not to be touched since it deals with the compressor only and has no business whatsoever with the fan. If at all defective, the silver one would be the one. The pics are not clear, but I think you have there a DUAL capacitor. If so, the cap itself has "3" terminals, labeled C, F, H (Common, Fan and Hermetic) or some similar terminology.

Mare sure to label the wires before you disconnect them from the capacitor terminals, just so you re-connect them in their proper places.

Disconnect the terminals with a pair of needle nose pliers that has an insulated handle, then, with the metal shaft of a screw driver touch terminals C-F and then C-H. Don't worry much about the charge, caps usually do not hold the charge for too long. But of course is always good to be extra cautious.


Check the wires that feed the fan motor for voltage. maybe there's a loose wire and the motor is not getting its juice.

Some high end units have a "cycling switch" that would keep the fan motor OFF for a few seconds until the pressure/temperature in the condensing unit rises to a level determined by the mfr. See if the power wires from the motor go straight to the contactor contacts or if perhaps they go to a small box (the switch).

What's the Mfr and M/N of this unit?

If the capacitor tests o.k. and you find no loose wires here, then the motor windings are shot.
 
 

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