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COOLING LOAD SATISFIED — Unit shuts down if cool-
ing load is satisfied. Unit restarts if required after comple-
tion of 5-minute timer cycle.
THERMISTOR FAILURE — If thermistor fails in open mode,
the temperature controller shuts down the unit in an out-of-
range condition. Replace the thermistor. Unit restarts auto-
matically after completion of a 5-minute timer cycle, and
when the leaving cooler chilled fluid temperature rises above
the upper deadband limit of the temperature controller.
NOTE: If the thermistor fails in closed mode, the tempera-
ture controller keeps trying to load up.
If unit stoppage occurs more than once as a result of
any of the safety devices listed, determine and correct
cause before attempting another restart.
Table 14 — Troubleshooting
SYMPTOMS CAUSE REMEDY
Compressor does
not run
Power line open Reset circuit breaker.
Control fuse or circuit breaker opens Check control circuit for ground or short. Reset breaker
and replace fuse.
Compressor overtemperature sensor open Find cause of high temperature and reset controls.
Tripped power breaker Check the controls. Find the cause of trip and
reset breaker.
Condenser circulating pump not running Power off — restart.
Pump binding — free pump.
Incorrect wiring — rewire.
Pump motor burned out — replace.
Loose terminal connection Check connections.
Improperly wired controls Check wiring and rewire if necessary.
Low line voltage Check line voltage — determine location of voltage drop
and remedy deficiency.
Compressor motor defective Check motor winding for open or short. Replace
compressor if necessary.
Seized compressor Replace compressor.
Compressor cycles
off on loss of
charge
Loss of charge control erratic in action Repair leak and recharge.
Replace control.
Low refrigerant charge Add refrigerant.
Low suction temperature Raise cooler leaving fluid temperature set point.
Compressor suction valve leaking Replace valve plate.
Plugged compressor suction strainer Clean or replace strainer.
Compressor suction shutoff valve partially closed Open valve.
Compressor cycles
off on out of range
condition
Thermistor failure Replace thermistor.
System load was reduced faster than
controller could remove stages
Unit will restart after fluid temperature rises back into the
control band. Avoid rapidly removing system load.
Compressor cycles control
steps rapidly
Temperature controller deadband setting is
too low
Raise deadband setting.
Compressor shuts
down on high-
pressure control
High-pressure control acting erratically Replace control.
Compressor discharge valve partially closed Open valve or replace (if defective).
Air in system Purge system.
Condenser scaled/dirty Clean condenser.
Receiver not properly vented — refrigerant
backs up into evaporator condenser
Repipe as required to provide adequate venting.
Condenser water pump or fans not operating Start pump — repair or replace if defective.
System overcharged with refrigerant Reduce charge.
Unit operates too long
or continuously
Low refrigerant charge Add refrigerant.
Control contacts fused Replace control.
Air in system Purge system.
Partially plugged or plugged expansion valve
or filter drier
Clean or replace as needed.
Defective insulation Replace or repair as needed.
Service load Keep doors and windows closed.
Inefficient compressor Check valves, and replace if necessary.
Unusual or loud system
noises
Piping vibration Support piping as required.
Check for loose pipe connections.
Expansion valve hissing Add refrigerant.
Check for plugged liquid line filter drier.
Compressor noisy Check valve plates for valve noise.
Replace compressor (worn bearings).
Check for loose compressor holddown bolts.
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