Diagnosis
165
Unit in vacuum—frost on
expansion valve only Ice plugging expansion valve screen
or orifice
Apply hot wet cloth to expansion
valve. Moisture indicated by increase
in suction pressure. Replace filter
drier
High suction pressure Overcharge of refrigerant Purge system
Expansion valve open too much Adjust or replace valve
Defective controller or main relay
board
Diagnose main relay board and
controller. Replace defective
component
Service gauge out of calibration Adjust or replace service gauge
Low suction pressure
NOTE: This unit has a suction
modulation capacity control
system. Suction and discharge
pressures may drop below
expected normal readings
when the unit is on
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
Iced or dirty evaporator coil Defrost or clean evaporator coil
Restricted lines Locate and clear restriction
Plugged filter drier Replace filter drier
Expansion valve closed too much Adjust or replace valve
Expansion valve feeler bulb
improperly mounted, poorly insulated
or making poor contact
Correct feeler bulb installation
Evaporator fans off
Check evaporator fan motors and
control circuit and correct fault
Defective controller or main relay
board
Diagnose main relay board and
controller. Replace defective
component
Service gauge out of calibration Adjust or replace gauge
Condition Possible Cause Remedy
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