5 TROUBLESHOOTING
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 no voltage,
check control setting requires cooling. If there is voltage, lockout relay
may be energized. Check for 24VAC at control connections 2 & 3. If
there is voltage, see compressor high-discharge pressure/lockout
relay.
Control voltage circuit breaker (at
transformer in evaporator module)
open
Locate short and reset circuit breaker.
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 pressure /
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.
Low compressor capacity/ no
cooling
Defective liquid line solenoid valve Check valve and coil; replace if necessary.
Plugged filter drier Check pressure drop across filter drier. Replace filter drier.
Low refrigerant charge
Check for normal system operating pressures. Refer to abnormal
pressure causes if applicable. Check for leaks. Proper refrigerant
charge is very important at low ambient operation.
Compressor noisy
Loose compressor or piping support Tighten clamps.
Compressor rotation in reverse
direction
Check for proper power phase wiring to unit and to compressor motor.
Pipe Rattle Loose pipe connections Check pipe connections.
Compressor running hot Compression ratio too high
Check for normal system operating pressures. Refer to abnormal
pressure causes if applicable.
Compressor motor protectors
tripping or cycling
High discharge pressure Check for blocked condenser fan or coil.
High suction temperature
Check expansion valve and hot gas bypass valve setting. Check liquid
quenching valve operation.
Loose power or control circuit wiring
connection
Check all power and control circuit connections.
Defective motor
Check for motor ground or short. Replace compressor if either
condition is found.
Table 5.1 Troubleshooting
Vertiv | Liebert PFH Installer/User Guide | 37
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