Getting 80v on 1 leg of air conditioner compressor.

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  #1  
Old 10-12-13, 09:34 PM
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Getting 80v on 1 leg of air conditioner compressor.

I was checking voltage on an air conditioner compressor this evening and ran into an issue. With the compressors disconnect switch in the off position, L1 has 120v to ground. When I meter between L1's live terminal in the disconnect box to L1's load terminal in the box (basically just bypassing the fuse), I get 80v. L2is normal with 120v line to ground, and 120v line to load.

I've heard of open neutrals, but this 240v circuit just has L1, L2, and ground. Is the problem with the ground instead of a neutral? I was using a true RMS meter.
 
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Old 10-12-13, 09:37 PM
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What is your voltage between Ln1 and Ln2?
 
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Old 10-12-13, 09:44 PM
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between the two I was around 200v.
 
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Old 10-12-13, 10:16 PM
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Measuring from line to load tells you absolutely nothing.

If you are measuring supply voltage you should see 240 VAC between hot legs and 120 VAC from each hot leg to ground.
 
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Old 10-12-13, 10:45 PM
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But I don't see 240V between L1 and L2.

You saying there is no indication of a problem when the potential difference between 120v line and load is not 120v?
 
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Old 10-13-13, 05:51 AM
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What is the voltage at the breaker panel?
 
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Old 10-13-13, 07:02 AM
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I'd also be interested in what readings you get, with the disconnect "OFF", at L1 to ground and L2 to ground on the "LOAD" side of disconnect.

Why are you checking voltages anyway, is there a problem with the unit?
 
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Old 10-13-13, 09:30 AM
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Wasn't able to check at the panel. I'll try that today.

With the disconnect off, L1 to ground was 120v. L1 load side to ground was 6VAC. L2 to ground was 120V and L2 load side to ground was 0V.

Reason I was checking the unit was to make sure there was 240v to the compressor and 24v to the relay. The temp inside was 81 while the thermostat was calling for air trying to cool down to 73.
 
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Old 10-13-13, 09:41 AM
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With the disconnect open.....anything you read on the load side is just induced or picked up from nearby sources or wire.

When you measure between L1 and L2 at the line side of the disconnect you should measure 240 VAC. If you don't then you need to work your way back to the panel.

If the disconnect is open..... then nothing on the load side of the disconnect will affect your 240v coming into the disconnect.
 
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Old 10-13-13, 09:41 AM
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Bet you are using a digital meter aren't you. If you have an analog multimeter use it instead.
 
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Old 10-13-13, 09:56 AM
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I agree.
You need to either an analog test meter or a high quality digital meter that most diy'ers can't justify owning.
 
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