62
Chapter 4
Step 6: Check Start Capacitor
CAUTION:
Using a 20,000 ohm resistor, discharge the
capacitor before removing it from the system to avoid damage
to measuring devices and risk of electric shock.
Disconnect
the start capacitor from the system. Use a capacitance meter to
measure the capacitance. The capacitance value should be the
rated value minus 0% to plus 20%. If it is outside of this range,
then the start capacitor needs to be replaced.
As an alternative, check the start capacitor by measuring conti-
nuity between relay terminals 1 and 2:
a. Rx1 scale: If there is continuity, then the start capacitor
is shorted and needs to be replaced.
b. Rx100,000 scale: If there is no needle deflection on an
analog meter or if a digital meter indicates infinite resis-
tance, then the start capacitor is open and needs to be
replaced.
Possible reasons that a start capacitor is not working properly
include:
•
Use of incorrect start capacitor. Replace with proper start
capacitor.
•
The relay contacts are not working properly. Replace
the relay.
•
Prolonged operation on start cycle due to low voltage.
Determine if the line voltage is too low (less than 90% of
rated voltage).
•
Prolonged operation on start cycle due to incorrect
relay. Replace with correct relay.
•
Prolonged operation on start cycle due to starting load
too high. Refer to the OEM service information to use
pump down arrangement, if necessary.
•
Excessive short cycling. Short cycling can be caused by
problems with the compressor’s thermal protector or sys-
tem components such as the thermostat, control, contac-
tor, or high or low pressure cut-out. For more information
on troubleshooting the thermal protector, see Step 3. For
troubleshooting the system components, refer to the OEM
service information.
Step 7: Check Wiring
Confirm that there is continuity between 2 and S and between
4 and R, then reconnect unit.
Step 8: Replace Potential Relay
If all above tests prove satisfactory, there is no capillary restric-
tion, and the unit still fails to operate properly, replace the relay.
The new relay will eliminate any electrical problems which can-
not be determined with above tests.
Step 9: Continue Troubleshooting
If the new relay does not correct the problem, check for ade-
quate compressor pumping as outlined in the procedure on
page 83.
