15
Troubleshooting Guide -
Tranquility
®
Digital (DXM2) Packaged Units
Rev.: 01/15/14
An Alternative Way of Checking Compressors
A-D
Application - Hermetic Motors
Hermetic motors require special test parameters since the
winding operates in an oil and refrigerant atmosphere.
Under normal conditions the oil and refrigerant have a high
electrical resistance. However, when they are contaminated
with moisture, the electrical resistance changes and a low
megohm reading of the winding terminal to ground may
actually be the resistance of the contaminants in the oil and
not in the winding insulation.
New hermetic motors have a resistance value of more than
100 megohms. Readings of 50 megohms or less would
indicate that either the winding insulation is deteriorating or
the oil/refrigerant is contaminated.
Installing an oversized drier may clean up the system or
another possible solution could be replacing all of the
compressor oil. In either case, if the megohm tests show
even the slightest improvement in resistance values, the
remedy may have checked a declining condition.
A good “rule of thumb” is to smell a small sample of the oil. If
at any time in the history of the unit the motor was severely
overloaded, it will leave a tell tale trace in the oil than can
be removed other than by discharging all the refrigerant and
replacing the oil.
The odor of burnt insulation is easily recognizable and a low
resistance value of 20 megohms or less will verify that the
motor insulation may be severely damaged.
Megohmmeter
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