GVZC20 Service Manual
SERVICING
24
NOTE: An optional method is to locate the thermometer
at the suction line service valve. Ensure the thermometer
makes adequate contact and is insulated for best possible
readings.
3. Refer to the superheat table provided for proper system
superheat. Add charge to lower superheat or recover
charge to raise superheat.
Superheat Formula = Suct. Line Temp. - Sat. Suct.
Temp.
EXAMPLE:
a. Suction Pressure = 143 PSIG
b. Corresponding Temp. = 50°F.
c. Thermometer on Suction Line = 58°F.
To obtain the degrees temperature of superheat, subtract
50.0 from 58.0°F.
The dierence is 8° Superheat. The 8° Superheat would
fall in the ± range of allowable superheat.
Refrigerant liquid is considered subcooled when its tem-
perature is lower than the saturation temperature corre-
sponding to its pressure. The degree of subcooling equals
the degrees of temperature decrease below the saturation
temperature at the existing pressure.
1. Attach an accurate thermometer or preferably a thermo-
couple type temperature tester to the liquid service valve
as it leaves the condensing unit.
2. Install a high side pressure gauge on the high side (liq-
uid) service valve at the front of the unit.
3. Record the gauge pressure and the temperature of the
line.
4. Review the technical information manual or specication
sheet for the model being serviced to obtain the design
subcooling.
5. Compare the hi-pressure reading to the “Required Liquid
Line Temperature” chart. Find the hi-pressure value on
the left column. Follow that line right to the column under
the design subcooling value. Where the two intersect is
the required liquid line temperature.
Alternately you can convert the liquid line pressure
gauge reading to temperature by nding the gauge read-
ing in the R-410A Pressure vs. Temperature Chart, nd
the temperature in the °F. Column.
6. The dierence between the thermometer reading and
pressure to temperature conversion is the amount of
subcooling.
Add charge to raise subcooling. Recover charge to lower
subcooling.
Subcooling Formula = Sat. Liquid Temp. - Liquid Line Temp.
NOTE: To adjust subcooling, follow the sequence of S-108.
EXAMPLE:
a. Liquid Line Pressure = 417 PSIG
b. Corresponding Temp. = 120°F.
c. Thermometer on Liquid line = 109°F.
To obtain the amount of subcooling subtract 109°F from
120°F.
The dierence is 11° subcooling. See the specication
sheet or technical information manual for the design sub-
cooling range for your unit.
There are other causes for high head pressure which may
be found in the “Cooling / Heating Analysis Chart.”
If other causes check out normal, an overcharge or a sys-
tem containing non-condensables would be indicated.
If this system is observed:
1. Start the system.
2. Remove and capture small quantities of gas from the
suction line dill valve until the head pressure is reduced
to normal.
3. Observe the system while running a cooling perfor-
mance test. If a shortage of refrigerant is indicated, then
the system contains non-condensables.
OD Ambient Temp
(degF)
<65°F 65°F to 105°F >105°F
Subcooling
(degF)
Weigh in
Charge
2T to 5T:8°F ±1°F
Weigh in
Charge
Charging Table
SUPERHEAT AND SUBCOOLING ADJUSTMENT ON TXV
APPLICATIONS
NOTE: Subcooling and superheat information is valid only
while the unit is operating at 100% capacity or 100% com-
pressor speed in CHARGE MODE.
Compressor speed is displayed under STATUS menu in the
thermostat.
1. Run system at least 10 minutes to allow pressure to
stabilize. During the adjustment of subcooling, ambient
temperature should be greater than 65°F and less than
105°F. If ambient temperature is out of range, don’t ad-
just subcooling.
2. For best results, temporarily install a thermometer on the
liquid line at the liquid line service valve and 4-6” from
the compressor on the suction line. Ensure the thermom-
eter makes adequate contact and is insulated for best
possible readings. Use liquid line temperature to deter-
mine sub-cooling and vapor temperature to determine
superheat.
NOTE: An optional method is to locate the thermometer at
the suction line service valve. Ensure the thermometer
makes adequate contact and is insulated for best possi-
ble readings.
3. The system subcooling should be 8°F ± 1°F(*1). If not in
that range, adjust subcooling and superheat according to
the following procedure.
a. If subcooling and superheat are low, adjust TXV to 7
to 9°F superheat, then check subcooling.
NOTE: To adjust superheat, turn the valve stem
clockwise to increase and counter clockwise to de-
crease.
b. If subcooling is low and superheat is 7 to 9°F, add
charge to rise subcooling to 8°F ± 1°F(*1), then check
superheat.
c.If subcooling is low and superheat is high, add charge