Parallel Compressor Systems Installation & Operations Manual, October 2004
35
Symptom
Cause
Remedy
Low
Discharge
Pressure
1.
2.
3.
4.
5.
Insufficient refrigerant in system
Faulty condenser temp. regulation
Compressor suction or discharge valve inefficiencies
Low suction pressure
Head pressure control valve set wrong
or no head pressure control valve
1.
2.
3.
4.
5.
Check for leaks. Repair and add charge
Check condenser control operation
Clean or replace leaky valve plates
See corrective steps for low suction pressure
Adjust valve or install a head pressure control valve
High Suction
Pressure
1.
2.
Excessive load
Expansion valve overfeeding
1.
2.
Reduce load or add additional equipment
Check remote bulb. Regulate superheat
Low Suction
Pressure
1.
2.
3.
4.
5.
6.
7.
Lack of refrigerant
Evaporator dirty or iced
Clogged liquid line filter drier
Clogged suction line or compressor
suction strainer
Expansion valve malfunctioning
Condensing temperature too low
Improper TXV
1.
2.
3.
4.
5.
6.
7.
Check for leaks. Repair and add charge
Defrost or clean coil
Replace cartridge(s)
Clean strainer or replace filters
Check and reset for proper superheat
Check means for regulating
condensing temperature
Check for proper sizing
Little or No
Oil Pressure
1.
2.
3.
4.
5.
6.
7.
8.
9.
Clogged suction oil strainer
Excessive liquid in crankcase
Low oil pressure safety switch defective
Worn oil pump
Oil pump reversing gear stuck in
the wrong position
Low oil level
Worn bearings
Loose fitting on oil lines
Pump house gasket leaks
1.
2.
3.
4.
5.
6.
7.
8.
9.
Clean
Check crankcase heater. Reset TXV for
higher superheat. Check liquid line solenoid
valve for proper operation.
Replace
Replace
Reverse direction of compressor rotation
Determine where the oil is or add oil
Replace compressor
Check and tighten fittings
Replace gasket
Compressor
Loses Oil
1.
2.
3.
4.
Lack of refrigerant
Excessive compression ring blowby
Refrigerant floods back
Improper piping or traps
1.
2.
3.
4.
Check for leaks. Repair and add charge
Replace compressor
Maintain proper superheat at compressor
Correct piping
Compressor
Thermal
Protector
Switch Open
1.
2.
3.
4.
5.
Operating beyond design limits
Discharge valve partially shut
Blown valve plate gasket
Dirty condenser coil
Overcharged system
1.
2.
3.
4.
5.
Add facilities so that conditions are within
allowable limits
Open valve
Replace gasket
Clean coil
Reduce charge
Parallel Compressor Systems
