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Electric Standby Mechanical Diagnosis
CONDITION POSSIBLE CAUSE REMEDY
Compressor does not run Improperly wired Check wiring against diagram
Low line voltage Check line voltage—determine
location of voltage drop
Relay contacts not closing Check and replace relay if defective
Open circuit in motor winding Check motor leads. If leads OK,
replace motor
High pressure cutout switch open Eliminate cause of excessive
pressure
Thermostat faulty Repair or replace
Compressor piston stuck Replace compressor
Frozen compressor or motor
bearings
Repair or replace
Shortage of refrigerant Check for leaks, repair as required,
and recharge
Low pressure cutout switch open Check and replace if necessary.
Overload relay open Turn On-Off switch OFF and back
ON
Unit short cycles Shortage of refrigerant (low pressure
cutout)
Repair leak and recharge
Restricted expansion valve (low
pressure cutout)
Replace expansion valve
Refrigerant overcharge (high
pressure cutout)
Remove excess charge
Cycling on high pressure cutout Check air flow and fan
Clogged condenser coil Clean coil
Motor contactor burnout Low line voltage Increase voltage (must be ± 10% of
compressor motor rating)
Excessive line voltage Reduce voltage (must be ± 10% of
compressor motor rating)
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