Testing HVAC Electrical/Compressor


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Old 04-18-19, 06:41 PM
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Testing HVAC Electrical/Compressor

Tested Amp Draw on my split AC

Compressor Common 20.5 Run 16.9 Start 7.8

Fan Common 1.16 Run 1.3 Start 1.03

Compressor RLA 29.1
Fan FLA 1.9


This is an older system.

I realize temp play a factor on everything but my concern/curiosity is more the percentage diff between the legs of the common and run lines. Does anything look out of whack?

Voltage under load 233v, no load 235v (at contactor)
 
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Old 04-18-19, 07:21 PM
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Not sure what you are asking. Since this is 240vAC....... there really is no common. You have two legs of power. The current you measure should be the same on either leg.

I wouldn't be overly concerned with the start amperage..... the run amperage is what's important.
Compressor current of 16.9A is ok.
Fan current of 1.3A is ok too.

A voltage drop of 2v with the unit running and not running is great. Minimal drop.
 
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Old 04-18-19, 09:01 PM
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Common here refers to the common line on on the motors (not common on feed lines). Motor schematics show a common, start winding and run winding. Yes the voltage looks great, I just added that to show there was no voltage drop. On the two feed lines they both show the same amperage, so yes that is okay.

So is it fair to say there is no way to compare the relationship between the three lines to the motors without knowing the winding resistance?

I added a start assist 5-2-1 and was just curious to see if there was any visible benefit. My meter doesn't capture inrush.

What would be the best way to test that the start assist relay is releasing after the unit turns on?

Also, notice when checking voltage to the 5-2-1, it approx 120 on each relay terminal when the ac is shut off, but when running the "2" terminal voltage reads in the 300??
 
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Old 04-18-19, 09:16 PM
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If the start relay wasn't releasing..... your compressor would not like it and you'd know quickly.
 
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Old 04-19-19, 04:49 AM
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Is there a problem for you to be checking this?

The readings are prefectly normal.
On the compressor and after it starts, between common and run you will see the running amperage.
Between common and start you have the amperage that is bled through the run capacitor for added efficiency.
In all cases a run capacitor bleeds current to the start winding and is used for starting if there is no relay.
The MFD rating of the capacitor controls how much current and is determined by the mfr.
If the contacts on the relay were stuck you would have full starting current which would exceed the running amperage.
 
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Old 04-19-19, 03:10 PM
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Is there a problem for you to be checking this?
No, Just trying to evaluate my system plus I added the 5-2-1 so just checking it out. Except for any charge issues and furnace inspections I like to run through what they do on those "$79 Checkups" just for piece of mind.


If the contacts on the relay were stuck you would have full starting current which would exceed the running amperage.
Concluded that this is not occurring.
 
 

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