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7) If the superheat is high, check the subcooling first to know if the refrigerant
charge is sufficient. If the charge is not sufficient, add more refrigerant. If the
charge is good, then increase the evaporator suction pressure by turning the
hex nut (5/16”) clockwise. Liquid must always be charged into the hide side
when the compressor runs.
8) If the superheat is low, then decrease the evaporator suction pressure by
turning the hex nut (5/16”) counter-clockwise.
9) Both discharge and suction valves must be in the back positions before
disconnecting.
10) Close all service valves and disconnect all manifolds and hoses.
Fig. 15 Expansion Valve
10. Pressure, Superheat and Subcooling Readings
CAUTION:
To read properly the service valves must be in the middle positions.
Complaint Possible
Causes
1) High suction pressure and low head pressure
Zero superheat and zero subcooling
2) High suction pressure and low head pressure
Low superheat and low subcooling
3) High suction pressure and high head pressure
Low superheat and high subcooling
4) High to normal suction pressure and high head
pressure
Low subcooling
5) High suction pressure and high head pressure
Low superheat and low subcooling
6) High suction pressure and high head pressure
High superheat
7) Low suction pressure and low head pressure
High superheat and low subcooling
8) Low suction pressure and low to normal head
pressure
High superheat and high subcooling
9) Low suction pressure and low head pressure
1) Compressor may be bad
2) Expansion valve opened, too
much oil
3) Overcharge
4) Non-condensable
gas
5) Air restricted, dirty condenser,
bad condenser fans
6) High cellar temperature, high
evaporator load
7) Undercharge
8)
Liquid line restricted after
receiver, solenoid valve restricted
9) Suction line restricted
