58
Chapter 4
Step 1: Before Continuing with
Troubleshooting...
WARNING!
All electric power should be disconnected and
you should have already made sure that the compressor does
not have a ground fault (see “Checking for a Ground Fault”
on pages 47-48)
.
You should have also checked the windings
for continuity and proper resistance (see “Checking for Conti-
nuity and Proper Resistance” on pages 48-49), made sure the
system is getting proper voltage, and that the control, thermo-
stat, and contactor are working properly.
Step 2: Disconnect Fan Motor or Any
Other Devices
If there is a fan motor or any other auxiliary device, open the
circuit for the fan motor or any other device.
Step 3: Check External Thermal
Protector
Check for continuity across the thermal protector. If there is no
continuity, then the thermal protector may be tripped. Wait at
least 5 minutes, then check continuity again. If there is still no
continuity, replace the thermal protector.
Step 4: Check Current Relay
Keep the relay upright. Check the relay by measuring continuity
between:
a. Relay terminals 1 and S. If there is continuity, then the
relay contacts are closed when they should be open.
Replace the current relay.
b. Relay terminals 2 and M. If there is no continuity,
replace the current relay.
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 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.