Condenser fan motor always on (slowly)

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Old 05-15-14, 01:19 PM
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Condenser fan motor always on (slowly)

The fan on my Rheem 13AJA condensing unit is always on at a slow speed. It does go up to full speed when the thermostat calls for cooling. When that happens, I hear the compressor go on as well.

At first I thought it was the contactor but I tested that it is fine.

I am going to check the resistance across the fan terminals to make sure its not damaged. I'll test the capacitor too, but I don't think there is any problem with that. I'm thinking someone how the fan motor has 120V all the time and as a result spinning slowly.

Any other ideas?
 
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Old 05-15-14, 01:36 PM
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Welcome to the forum.

I'm thinking someone how the fan motor has 120V all the time and as a result spinning slowly.
You're half right. Many contactors only break one half of the 240v incoming live. That would mean that your motor has one leg always live. That motor developed a short in the windings and is actually running on 120v.

You would need to turn power off to the compressor unit. Now disconnect all three fan wires. Use an ohmmeter to check from each one to ground. You should not see any continuity.
(Be sure to label the fan wiring when disconnecting it)
 
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Old 05-15-14, 01:41 PM
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To your knowledge, has the fan motor ever been replaced? If it has been, perhaps a multi-speed motor was installed and was wired incorrectly.
 
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Old 05-15-14, 02:06 PM
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I bought this house recently, so I'm not sure if the fan motor was replaced. However, the part # on the motor matches what's supposed to be in there.

I hope its the fan motor and nothing else.
 
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Old 05-15-14, 03:17 PM
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If it's the correct motor (which it likely is from what you said), then it's probably what PJmax described. If you have an ohmmeter, it's relatively easy to check the motor for a shorted winding.
 
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Old 05-15-14, 05:25 PM
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I disconnected all 3 fan motor wires and measured continuity to ground. Nothing.

I measured the resistance between each pair of fan motor wire and found 60 ohms, 65 ohms, and 125 ohms. I understand this is what I should expect for a working fan motor.

Then, I started to put everything back together and started to think that the black wire (going to the hot side of the contactor) had to be going to ground somehow.

I discovered that the black wire had continuity to ground if (and only if) the brown motor fan wire was connected to the capacitor (to the fan terminal). What does this mean? The capacitor looks good to me (no bulging), but could it somehow be doing this?
 
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