18
19
Single Phase Resistance Test
Remove the leads from the compressor terminals and set
the ohmmeter on the lowest scale (R x 1).
Touch the leads of the ohmmeter from terminals common
to start ("C" to "S"). Next, touch the leads of the ohmmeter
from terminals common to run ("C" to "R").
Add values "C" to "S" and "C" to "R" together and
check resistance from start to run terminals ("S" to "R").
Resistance "S" to "R" should equal the total of "C" to "S"
and "C" to "R."
In a single phase PSC compressor motor, the highest value
will be from the start to the run connections (“S” to "R").
The next highest resistance is from the start to the common
connections ("S" to "C"). The lowest resistance is from the
run to common. ("C" to "R") Before replacing a compressor,
check to be sure it is defective.
Check the complete electrical system to the compressor and
compressor internal electrical system, check to be certain
that compressor is not out on internal overload.
Complete evaluation of the system must be made whenever
you suspect the compressor is defective. If the compressor
has been operating for some time, a careful
examination
must be made to determine why the compressor failed.
Many compressor failures are caused by the following
conditions:
1. Improper air flow over the evaporator.
2. Overcharged refrigerant system causing liquid to be
returned to the compressor.
3. Restricted refrigerant system.
4. Lack of lubrication.
5. Liquid refrigerant returning to compressor causing oil
to be washed out of bearings.
6. Noncondensables such as air and moisture in
the system. Moisture is extremely destructive to a
refrigerant system.
Recommended procedure for
compressor replacement
NOTE: Be sure power source is off, then disconnect all
wiring from the compressor.
1. Be certain to perform all necessary electrical and
refrigeration tests to be sure the compressor is actually
defective before replacing .
2. Recover all refrigerant from the system though
the process tubes.
PROPER HANDLING OF
RECOVERED REFRIGERANT ACCORDING TO EPA
REGULATIONS IS REQUIRED.
Do not use gauge
manifold for this purpose if there has been a burnout.
You will contaminate your manifold and hoses. Use a
Schrader valve adapter and copper tubing for burnout
failures.
3. After all refrigerant has been recovered, disconnect
suction and discharge lines from the compressor and
remove compressor. Be certain to have both suction
and discharge process tubes open to atmosphere.
