Nordic ATWC Series, Installation And Service Manual, Page: 62 / 106

PRELIMINARY: 24-Sep-2021 Page 62 002536MAN-00
COMPRESSOR TROUBLESHOOTING
Fault
Possible Cause Verification Recommended Action
Compressor will
not start:
Stage 1 - R410a or
Stage 2 - R134a
Faulty control board. No 24vac output on STAGE1 or
STAGE2 when compressor should
be operating.
Replace control board.
Faulty run capacitor.
(Single phase only)
Check value with capacitance meter.
Should match label on capacitor.
Compressor will hum while trying to
start and then trip its overload.
Replace if faulty.
Loose or faulty wiring. Check all compressor wiring, includ-
ing inside compressor electrical box.
Fix any loose connections. Re-
place any damaged wires.
Faulty compressor
contactor.
Voltage on line side with contactor
held closed, but no voltage on one
or both terminals on the load side.
Points pitted or burned.
Or, 24VAC across coil but contactor
will not engage.
Replace contactor.
Thermal overload on
compressor tripped.
Ohmmeter shows reading when
placed across R and S terminals
and infinity between C & R or C & S.
A valid resistance reading is present
again after the compressor has
cooled down.
Proceed to Operation Trouble-
shooting to determine the cause
of the thermal overload trip.
Burned out motor
(open winding)
Remove wires from compressor.
Ohmmeter shows infinite resistance
between any two terminals. Note:
Be sure compressor overload has
had a chance to reset. If compressor
is hot this may take several hours.
Replace the compressor.
Burned out motor
(shorted windings)
Remove wires from compressor.
Resistance between any two termi-
nals is below the specified value.
Replace the compressor.
Motor shorted to ground. Remove wires from compressor.
Check for infinite resistance be-
tween each terminal and ground.
If any terminal to ground is not
infinite replace the compressor.
Seized compressor due to
locked or damaged
mechanism.
Compressor attempts to start but
trips its internal overload after a few
seconds. (Run capacitor already
verified)
Attempt to “rock” compressor
free. If normal operation cannot
be established, replace
compressor.
Compressor starts
hard
Start capacitor faulty.
(Single phase only)
Check with capacitance meter.
Check for black residue around
blowout hole on top of capacitor.
Replace if faulty.
Remove black residue in electri-
cal box if any.
Potential relay faulty.
(Single phase only)
Replace with new one and verify
compressor starts properly.
Replace if faulty.
Compressor is “tight” due
to damaged mechanism
Compressor attempts to start but
trips its internal overload after a few
seconds. Run capacitor has been
verified already.
Attempt to “rock” compressor
free. If normal operation cannot
be established, replace com-
pressor.