Diagnosis
164
Head pressure too low
NOTE: This unit has a suction
modulation capacity control
system. Suction and discharge
pressures may drop below
expected normal readings
when the unit is in Modulation
Cool (control temperature
within 10 C [18 F] of setpoint
or in Power Limit mode).
Shortage of refrigerant Repair leak and recharge
Low ambient air temperature No remedy
Service gauge out of calibration Replace gauge
Head pressure too high Refrigerant overcharge Purge system
Air in refrigeration system Evacuate and recharge
Dirty or restricted condenser coil Clean condenser coil
Condenser fan not operating
See “Condenser Fan Motor Does Not
Operate” under “Mechanical
Diagnosis”
Condenser fan grille damaged or
missing
Repair or replace grille
Condenser fan blade damaged Replace fan blade
High ambient air temperature No remedy
Restricted dehydrator or high side Replace filter drier or clear restriction
Defective service gauge Replace gauge
Compressor loses oil Refrigerant leak Repair leak and recharge
Compressor oil migrates to
system
Short cycling
See “Unit Short Cycles” under
“Mechanical Diagnosis”
Rapid cycling between Cool,
Null and Heat modes
Air short cycling through evaporator Check and correct cargo load
Defective controller or main relay
board
Diagnose main relay board and
controller. Replace defective
component
Short cycling
See “Unit Short Cycles” under
“Mechanical Diagnosis”
Stepper motor valve stuck close or
defective
Replace valve
Hot liquid line Shortage of refrigerant Repair or recharge
Expansion valve open too wide Adjust or replace expansion valve
Frosted liquid line Liquid line restricted Remove restriction
Restricted filter drier Replace filter drier
Frosted or sweating suction
line
Expansion valve admitting excess
refrigerant
Check feeler bulb and adjust
expansion valve
Evaporator coil needs defrosting
Check defrost circuit including
controller and evaporator coil sensor
Evaporator fan does not operate
See “Evaporator Fan Motor Does Not
Operate” under “Mechanical
Diagnosis”
Warm gas bypass valve open
Normal when unit is in Modulation
and container temperature is near
setpoint
Condition Possible Cause Remedy
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