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Condensing Unit Troubleshooting
Problem
Compressor will not run.
Problem
Compressor noisy or vibrating
High discharge pressure
Low discharge pressure
High suction pressure
Low suction pressure
Possible Cause
Main switch open
Fuse blown
Thermal overloads tripped
Defective contactor or coil
System shut down by safety devices
No cooling required
Liquid line solenoid will not open.
Low pressure switch will not close.
Motor electrical trouble
Possible Cause
Loose wiring
Flooding of refrigerant into crankcase
Improper pipe support
Worn compressor
Non-condensable in system
System overcharged with refrigerant
Discharge shut-off valve partially closed
Fan not running
Insufficient condenser air supply
Dirty condenser coil
Faulty head pressure control
Suction shut-off valve partially closed
Insufficient refrigerant in system
Low suction pressure
Excessive load
Expansion valve overfeeding
Lack of refrigerant
Evaporator dirty or iced
Clogged liquid line or suction line filter-
drier
Expansion valve malfunctioning
Condensing temperature too low
Improper TXV
Corrective Action
Close switch
Check electrical circuits and motor
winding for shorts or grounds.
Investigate for possible overloading.
Replace fuse after fault is corrected.
Overloads are automatically reset.
Check unit closely when unit comes
back on line.
Repair or replace
Determine type and cause of shutdown
and correct
None. Wait until cooling is required.
Repair or replace coil.
Replace switch
Check motor for open windings or short
circuit.
Corrective Action
Check all wire junctions. Tighten all
terminal screws.
Check superheat setting of expansion
valve
Relocate or add hangers
Replace compressor
Recover, evacuate and charge
Remove excess charge
Open valve
Check electrical circuit or replace
defective fan motor
Check for cause and correct
Clean coil
Check head pressure control operation.
Open valve
Locate and repair leak, recover,
evacuate and recharge
Check for proper refrigerant charge
Reduce load or add additional
equipment
Secure and insulate TXV bulb or if
required adjust superheat.
Locate and repair leak, recover,
evacuate and charge.
Clean
Replace filter-drier
Check and reset for proper superheat
Check head pressure control
Check for proper sizing
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