Specifications

U-5 IOM 17
Guidelines for refrigerant circuit diagnosis
Normal Conditions
Subcooling: 10 to 12 F
Superheat: 8 to 12 F
Discharge: 140 to 150 F
Head Pressure: 210#
Suction Pressure: 70#
Evap. Temperature: 38 to 55 F, or 10-20 F below
leaving air temperature
Over-Charged Unit
Subcooling: 20 to 25 F
Superheat: 8 to 12 F
Discharge: 120 to 130 F
Head Pressure: 220# or higher than normal
Suction Pressure: 80# or higher than normal
Under-Charged Unit
Subcooling: 6 to 8 F or lower than normal
Superheat: 25 to 30 F or higher than
normal
Discharge: Over 200 F
Head Pressure: 180# or lower than normal
Suction Pressure: 25# if lost a lot of refrigerant
Other: Lower than normal evaporative
temperature
Plugged Thermal Expansion Valve
Subcooling: 15 to 20 F or higher than
normal
Superheat: 25 to 30 F or higher than
normal
Discharge: +200 F or warmer than normal
Head Pressure: 250# or higher than normal
Suction Pressure: 45# or lower than normal
Other: May have frost on air coil
May have high leaving air
temperature
The air coil may not be wet
Low Evaporator Temperature
● Undercharged.
● Poor refrigerant distribution.
● Low airflow (clogged filter or air coil).
● Excess oil in refrigerant air bypassing the coil.
● Damaged fins on the coil or poor fin-to-tube bond.
Subcooling in Cooling Mode
● Subcooled refrigerant is found after the coax and
before the TXV.
● The liquid line is almost always subcooled.
● The liquid line should be several degrees colder
than the leaving water temperature.
● Superheated refrigerant is found after the air coil
and before the compressor.
● Superheated refrigerant is found after the
compressor and before the coax.
High Suction Superheat
● Under-charged refrigerant circuit.
● Poorly adjusted TXV — open it.
● Plugged TXV.
● High entering air temp in the cooling mode.
Poorly insulated suction line.
Low Suction Superheat
● Over-charged refrigerant circuit.
● Poorly adjusted TXV — close it.
● Low entering air temp in the cooling mode.
● Low airflow in the cooling mode.
Discharge Superheat
● High discharge superheat:
High suction superheat
Compressor lubrication problems
Compressor electrical problems
● Low discharge superheat:
Low suction superheat
Flooding-back