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FIELD TROUBLESHOOTING
IF THE COMPRESSOR WILL NOT
RUN
1. If there is no voltage at the compressor
terminals, follow the wiring diagram
and check back from compressor to
the power supply to find where the cir-
cuit is interrupted.
2. If power is available at the compressor
terminals, and the compressor does
not run, check the voltage at the com-
pressor terminals while attempting to
start the compressor.
If voltage at the compressor terminals
is below 90% of the nameplate volt-
age, it is possible the motor may not
develop sufficient torque to start.
Check to determine if wire sizes are
adequate, electrical connections are
loose, the circuit is overloaded, or if
the power supply is inadequate.
3. On single phase compressors, a defec-
tive capacitor or relay may prevent the
compressor starting. If the compres-
sor attempts to start but is unable to do
so, or if there is a humming sound,
check the relay to see if the relay con-
tacts are damaged or fused. The relay
points should be closed during the ini-
tial starting cycle, but should open as
the compressor comes up to speed.
Remove the wires from the starting
relay and capacitors. Use a high volt-
age ohmmeter to check for continuity
throughout the relay coil. Replace the
relay if there is not continuity. Use an
ohmmeter to check across the relay
contacts. Potential relay contacts are
normally closed when the relay is not
energized, current relay contacts are
normally open. If either gives an
incorrect reading, replace the relay.
Any capacitor found to be bulging, leak-
ing, or damaged should be replaced.
Make sure capacitors are discharged
before checking. Check for continuity
between each capacitor terminal and
the case. Continuity indicates a short,
and the capacitor should be replaced.
Substitute a “known to be good” start
capacitor if available. If compressor
then starts and runs properly, replace
the original start capacitor.
If a capacitor tester is not available, an
ohmmeter may be used to check run
and start capacitors for shorts or open
circuits. Use an ohmmeter set to its
highest resistance scale, and connect
prods to capacitor terminals.
a) With a good capacitor, the indicator
should first move zero, and then grad-
ually increase to infinity.
b) If there is no movement of the ohm-
meter indicator, an open circuit is indi-
cated.
c) If the ohmmeter indicator moves to
zero, and remains there or on a low
resistance reading, a short circuit is
indicated. Defective capacitors
should be replaced.
4. If the correct voltage is available at the
compressor terminals, and no current
is drawn, remove all wires from the
terminals and check for continuity
through the motor windings. On sin-
gle phase motor compressors, check
for continuity from terminals C to R,
and C to S. On compressors with line
break inherent protectors, an open
overload protector can cause a lack of
continuity. If the compressor is warm,
wait one hour for the compressor to
cool and recheck. If continuity cannot
be established through all motor wind-
ings, the compressor should be
replaced.
Check the motor for ground by means
of a continuity check between the
common terminal and the compressor
shell. If there is a ground, replace the
compressor.
5. If the compressor has an external pro-
tector, check for continuity through
the protector or protectors.
All external inherent protectors on
compressors can be replaced in the
field.
I F THE MOTOR COMPRESSOR
S TA RTS BUT TRIPS REPEAT E D LY
ON THE OVERLOAD PROTECTO R
1. Check the compressor suction and dis-
charge pressures while the compressor
is operating. Be sure the pressures are
within the limitations of the compres-
sor. If pressures are excessive it may
be necessary to clean the condenser,
purge air from the system, replace
crankcase pressure regulating valve.
An excessively low suction pressure
may indicate a loss of charge.
On units with no service gauge parts
where pressures can be checked,
check condenser to be sure it is clean
and fan is running. Excessive temper-
atures on suction and discharge line
may also indicate abnormal operating
conditions.
2. Check the line voltage at the motor
terminals while the compressor is
operating. The voltage should be
within 10% of the nameplate voltage
rating. If outside those limits, the
voltage supply must be brought within
the proper range, or a motor compres-
sor with different electrical character-
istics must be used.
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