icetro IM Series, Technician'S Handbook

Page: 118 / 166

DIAGNOSING START COMPONENTS
If the compressor attempts to start, or hums and trips the
overload protector, check the start components before
replacing the compressor.
Capacitor
Visual evidence of capacitor failure can include a bulged
terminal end or a ruptured membrane. Do not assume a
capacitor is good if no visual evidence is present. A good
test is to install a known good substitute capacitor. Use a
capacitor tester when checking a suspect capacitor. Clip
the bleed resistor off the capacitor terminals before
testing.
Relay
The relay has a set of contacts that connect and
disconnect the start capacitor from the compressor start
winding. The contacts on the relay are normally closed
(start capacitor in series with the start winding). The relay
senses the voltage generated by the start winding and
opens the contacts as the compressor motor starts. The
contacts remain open until the compressor is de-
energized.
RELAY OPERATION CHECK
1. Disconnect wires from relay terminals.
2. Verify the contacts are closed.
Measure the resistance between terminals 1 and
2. No continuity indicates open contacts. Replace
the relay.
3. Check the relay coil.
Measure the resistance between terminals 2 and
5. No resistance indicates an open coil. Replace
the relay.
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