A LOOK AT SERVICE SAFETY
Servicing
69
Step 4: Check Potential Relay
Before checking the relay, be sure it is mounted at the proper
position. (See pages 28-32.) Check the potential relay by mea-
suring continuity between:
a. Relay terminals 5 and 2. If there is no continuity, replace
the relay.
b. Relay terminals 2 and 1. If there is no continuity, then
the contacts are open. Replace the relay.
Possible reasons that a relay is not working properly include:
•
Use of incorrect relay. Replace with correct relay.
•
Line voltage is too high or low (greater than 110% or
less than 90% of rated voltage).
•
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 5. For
troubleshooting the system components, refer to the OEM
service information.
•
Vibration due to loose relay mounting. Tighten relay
mounting.
•
Use of incorrect run capacitor. Replace with proper run
capacitor.
Step 5: 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 4:
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.
