Superheat; (Units With Txv Device); Subcooling - Daikin APGM3 Service And Troubleshooting

SERVICING

SUPERHEAT

Before checking the superheat or replacing the valve,
perform all the procedures outlined under Air Flow,
Refrigerant Charge, Expansion Valve - Overfeeding,
Underfeeding. These are the most common causes for
evaporator malfunction.
Checking Superheat
Refrigerant gas is considered superheated when its
temperature is higher than the saturation temperature
corresponding to its pressure. The degree of superheat
equals the degrees of temperature increase above the
saturation temperature at existing pressure.
Procedure:
1. Run system at least 15-20 minutes to allow pressure
to stabilize.
2. Install a low side pressure gauge on the suction line
access fitting.
3. Temporarily install thermometer on suction (large) line
near compressor with adequate contact and insulate
for best possible reading.
4. Record the gauge pressure corresponding
temperature and the temperature of the suction line.
5. Refer to the superheat table for proper system
superheat. Add charge to lower superheat recover
charge to raise superheat.
Superheat Table
EXAMPLE:
a. Suction Pressure = 143
b. Corresponding Temp. °F. = 50
c. Thermometer on Suction Line = 59°F
To obtain the degrees temperature of superheat, subtract
50.0 from 59.0°F. The difference is 9° Superheat. The 9°
Superheat would fall in the ± range of allowable superheat.
SUPERHEAT = SUCTION LINE TEMP - SAT. SUCTION
TEMP.
(Units with TXV Devices)
All package units with TXV devices are charged using the
SUBCOOLING method at the liquid line. After subcooling is
checked it is recommended to check unit superheat at the
evaporator coil suction line.
Checking Subcooling
Refrigerant liquid is considered subcooled when its
temperature is lower than the saturation temperature
corresponding to its pressure. The degree of subcooling
equals the degrees of temperature decrease below the
saturation temperature at the existing pressure.
Procedure:
1. Attach an accurate thermometer or preferably a
thermocouple type temperature tester to the liquid line
close to the pressure switch.
2. Install a high side pressure gauge on the liquid access
fitting.
3. Record the gauge pressure and the temperature of
the line.
4. The difference between the thermometer reading and
pressure to temperature conversion is the amount of

subcooling.

SUBCOOLING FORMULA = SAT. LIQUID TEMP. -
LIQUID LINE TEMP.
EXAMPLE:
a. Liquid Line Pressure = 417
b. Corresponding Temp. °F. = 120°
c. Thermometer on Liquid line = 109°F.
To obtain the amount of subcooling, subtract
109°F from 120°F. The difference is 11° sub-
cooling. See the specification sheet or technical
information manual for the design subcooling
range for your unit.
See R410A Pressure vs. Temperature chart.
Expansion Valve (TXV) System
Two Speed Application (*PGM5)
Run the unit on high stage cooling for 15-20 minutes until
refrigerant pressures stabilize. Check charge with unit on
high stage.
Follow checking subcooling instructions
NOTE: The TXV provided is designed to meet the
specification requirements for optimum product
operation. "NO ADJUSTMENTS NEEDED TO TXV".
NOTE: Even though the compressor section of a scroll
compressor is more tolerant of liquid refrigerant,
continued floodback or flooded start conditions may
wash oil from the bearing surfaces causing premature
bearing failure.
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