The Hotline: 08/04/2003

July 31, 2003
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Suction Gauges

QUESTION:
By Leo Via E-mail

I was trying to charge a central air system. The gauge on the suction line reading went into the retard section of the gauge, while the gauge on the high-pressure side charging with R-22 read 110. I could not charge the system. Could you explain what happened?

ANSWER:
From Dan Kramer, P.E.
Specialist Grade
Member of RSES

You reported that the suction gauge went to “retard.” That means into the vacuum? The high side was 110-psi R-22. That corresponds to about 64 degrees F. I assume the compressor was running. If it was running, then why didn’t the compressor pull R-22 from the cylinder into the system and pump it into the high side? It should have done that even if the TXV or cap tube was plugged.

It’s possible that the valve was not opened on the can of R-22.

Motors

QUESTION:
From John West
Chesterfield, Va.

My question involves checking motors to ground. At what point would you say you have a good path to ground? I have heard that it can be less than 1.5 megohms. What would be the maximum voltage if you wanted to use a megger?

ANSWER:
By Denny Bush
A.O. Smith

The resistance to ground should be a minimum or greater-than number. Both resistance and testing voltage will vary with the rated voltage of the motor being tested.

Standards are covered in IEEE 43-1974, which may be ordered from the Institute of Electrical and Electronics Engineers (IEEE). Another source of information is The Plant Engineer’s Guide to Electric Motors by Richard L. Nailen, Barks Publications, 400 N. Michigan Ave., Chicago, Ill. 60611.

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Publication date: 08/04/2003

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