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True Food Service Equipment, Inc.
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 circuit is
interrupted.
2. If power is available at the compressor
terminals, and the compressor does not
run, check the voltage at the compressor
terminals while attempting to start the
compressor.
If voltage at the compressor terminals is
below 90% of the nameplate voltage, 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 defective capacitor or relay may
prevent the compressor starting. If the
compressor attempts to start but is
unable to do so, or if there is a humming
sound, check the relay to see if the relay
contacts are damaged or fused. The relay
points should be closed during the initial
starting cycle, but should open as the
compressor comes up to speed.
Remove the wires from the starting
relay and capacitors. Use a high voltage
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,
leaking, 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 gradually increase to infinity.
b) If there is no movement of the
ohmmeter indicator, an open circuit is
indicated.
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 single
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 windings, 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
protector, check for continuity through
the protector or protectors. All external
inherent protectors on compressors can
be replaced in the field.
IF THE MOTOR COMPRESSOR STARTS
BUT TRIPS REPEATEDLY ON THE
OVERLOAD PROTECTOR
1. Check the compressor suction and
discharge pressures while the compressor
is operating. Be sure the pressures are
within the limitations of the compressor.
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 temperatures 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 compressor with
different electrical characteristics must be
used.
3. Check the amperage drawn while the
compressor is operating. Under normal
operating conditions, the amperage
drawn will seldom exceed 110% of the
nameplate amperage. High amperage
can be caused by low damage, defective
running capacitors, or a defective starting
relay.
Continued on next page
MAINTENANCE, CARE & CLEANING
