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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”).
Single Phase Resistance Test
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.
ELECTRIC SHOCK HAZARD
WARNING
Turn off electric power before service or
installation. Extreme care must be used, if it
becomes necessary to work on equipment
with power applied.
Failure to do so could result in serious injury or
death.
Many compressor failures are caused by the following
conditions:
1. Improper air fl ow 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.
GROUND TEST
Use an ohmmeter set on its highest scale. Touch one
lead to the compressor body (clean point of contact as a
good connection is a must) and the other probe in turn
to each compressor terminal. If a reading is obtained the
compressor is grounded and must be replaced.
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 sometime, a careful examination
must be made to determine why the compressor failed.
Certain unit components operate at
temperatures hot enough to cause burns.
Proper safety procedures must be followed,
and proper protective clothing must be
worn.
Failure to follow this warning could result
in moderate to serious injury.
WARNING
BURN HAZARD
External Overload VPAK 9, 12, 18 K Btus
With power off, remove the leads from compressor termi-
nals. If the compressor is hot, allow the overload to cool
before starting check. Using an ohmmeter, test continu-
ity across the terminals of the external overload. If you
do not have continuity; this indicates that the overload is
open and must be replaced.
Internal Overload VPAK 24 K Btus
The overload is embedded in the motor windings to
sense the winding temperature and/or current draw. The
overload is connected in series with the common motor
terminal.
1. With no power to unit, remove the leads from the com-
pressor terminals. Allow motor to cool.
2. Using an ohmmeter, test continuity between terminals
C-S and C-R. If no continuity, the compressor overload is
open and the compressor must be replaced.
Internal Overload
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