Thermo King CRR-20, Maintenance Manual

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8-2 Mechanical Diagnosis Diagnosis
CRR-20 & CRR-40, September 1999
Condition Possible Cause Remedy
Compressor does not Piston stuck Remove compressor head. Look for broken
operate; excessive valve and jammed parts
amperage draw or
intermittent cycling
Seized or frozen compressor bearings Replace compressor
on overload
Improperly wired Check/correct wiring against wiring diagram
NOTE: Controller soft
starts the compressor
Low line voltage Check line voltage — determine location of
after a heat or defrost voltage drop
cycle, or when the unit
has been off for more
High head pressure Eliminate cause of high head pressure
than 8 hours. See
“Sequence of Operation”
Contacts in compressor contactor not Check by operating manually. Repair or
in
µµ
P-D Controller chapter closing completely replace
Open circuit in compressor motor Check motor stator connections. Check
winding stator winding for continuity. If open,
replace compressor
Defective compressor motor internal Replace thermal overload protector or
thermal overload protector compressor
Compressor contactor Low line voltage Increase line voltage to at least 90% of
burned out compressor motor rating
Excessive line voltage Reduce line voltage to at least 110% of
compressor motor rating
Short cycling Eliminate cause of short cycling
Unit short cycles Controller out of calibration Recalibrate (see Diagnosis Manual for
Thermoguard
µ
P-D Microprocessor
Controller, TK 41230)
Refrigerant overcharge causing Purge system
cycling on high pressure cutout
Inefficient condenser operation Check condenser airflow, condenser
causing cycling on high pressure fan motor, condenser fan grille, condenser
cutout fan pressure switch, water pressure switch
(option), water flow rate (option) and \
water-cooled condenser-receiver tank
(option)