9 TROUBLESHOOTING
Table 9.1 below, lists problems you may encounter, the possible cause, and a suggested remedy.
Problem Cause Remedy
Unit will not start
No power to unit Check voltage at input terminal block.
Compressor contactor
not pulling in
Check for 24VAC±2VAC at control connections 1 & 2.
If there is voltage, then:
• Check 24VAC at control connections 3 and 6. If there is voltage,
then there is compressor high discharge pressure situation. The
compressor will attempt to start once the high-pressure situation
has resolved.
• Check 24 VAC at control connections 5 and 6. If there is no voltage,
then there is high discharge temperature situation. The
compressor will attempt to start once the high-temperature
situation has resolved and minimum 30 min have elapsed.
If there is no voltage between 1 & 2, then:
• Check control settings for cooling requirement.
• Check 24 VAC at control connections 3 and 6. If there is voltage,
there is compressor lock-out due to high discharge pressure
condition. Check display for high pressure alarm. Set S302 to 0 or
recycle power to indoor unit.
• Check 24VAC at control connections 5 and 6. If there is no voltage,
there is compressor lock-out due to high discharge temperature
condition. Check display for high temperature alarm. Set S303 to 0
or recycle power to indoor unit.
Control voltage fuses (at
transformer in evaporator
module) open
Locate short and replace fuses.
Short cycle prevention
control
Control software delays compressor 3 minutes from stop to start.
Compressor high
discharge pressure/
lockout relay
Check for 24VAC ±2VAC at control connections 2 & 3. Remove 24VAC signal at
Connection 2 by turning indoor unit control off, then back on, or by raising the
setpoint to remove the cab for cooling, then resetting to re-establish operation.
High discharge
pressure
Insufficient air flow across
condenser coil
Check fan operation. Remove debris from coil and air inlets.
High refrigerant charge Check refrigerant charge.
Low discharge
pressure
Faulty head pressure
control valve
Replace if defective.
Compressor rotation in
reverse direction
Check for proper power phase wiring to unit and to compressor motor.
Low suction
pressur/compressor
cycling
Insufficient refrigerant in
system
Check for leaks; repair and add refrigerant.
Plugged filter drier Replace filter drier.
Improper superheat
adjustment
Reset expansion valve for 10-15°F (5.6 to 8.4°C) superheat at evaporator.
Defective liquid line
solenoid valve
Check valve and coil; replace if necessary.
Table 9.1 Troubleshooting
9 Troubleshooting 31
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