11
EXPANSION VALVE SYSTEM
NOTE: Units matched with indoor coils equipped
with a TXV should be charged by Subcooling only.
SUBCOOLING FORMULA = SATURATED LIQUID LINE
TEMPERATURE - LIQUID LINE TEMPERATURE
1.
Purge gauge lines. Connect service gauge manifold
to base-valve service ports. Run system at least 10
minutes to allow pressure to stabilize.
2. Clamp a pipe clamp thermometer on the liquid line
near the liquid line service valve and 4-6" from the
compressor on the suction line.
a.
Ensure the thermometer makes adequate contact
to obtain the best possible readings.
b. The temperature read with the thermometer
should be lower than the saturated condensing
temperature.
3.
The difference between the measured saturated
condensing temperature and the liquid line
temperature is the liquid Subcooling value.
4. TXV-based systems should have a Subcooling value
of 8°F +/- 1°F.
5. Add refrigerant to increase Subcooling and remove
refrigerant to decrease Subcooling.
NOTE: Units matched with indoor coils equipped
with a TXV should be charged by Subcooling only.
Superheat can also be utilized to best verify
charge levels with an adjustable TXV and make
adjustments when needed in unique applications
due to refrigerant line length, differences in
height between the indoor and outdoor unit and
refrigerant tubing sizes. These adjustments
should only be performed by qualified service
personnel.
Superheat Settings for Expansion Valve System
Tonnage
SH at Compressor
1.5
14°F +/- 1°F
2
11°F +/- 1°F
2.5
9°F +/- 1°F
3
9°F +/- 1°F
3.5
9°F +/- 1°F
4
9°F +/- 1°F
5
9°F +/- 1°F
ADVANCED ADJUSTMENT
RECOMMENDATIONS
NOTE: Units matched with indoor coils equipped
with a TXV should be charged by Subcooling only.
SUPERHEAT FORMULA = SUCTION LINE
TEMPERATURE - SATURATED SUCTION
TEMPERATURE
1. Clamp a pipe clamp thermometer near the suction line
4-6” from the compressor on the suction line.
a.
Ensure the thermometer makes adequate contact
for the best possible readings.
b. The temperature read with the thermometer
should be higher than the saturated suction
temperature.
2.
The difference between the measured saturated
suction temperature and the suction line temperature
is the Superheat value.
3. TXV-based systems should have a Superheat value
as shown in the table below.
4. Adjust Superheat by turning the TXV valve stem
clockwise to
increase
and
counterclockwise
to
decrease
.
a. If Subcooling and Superheat are low,
adjust
the
TXV to the superheat setting specified in the table
below and then check Subcooling.
b. If Subcooling is low and Superheat is high,
add
charge to
raise
Subcooling to 8°F +/- 1°F then
check Superheat.
c. If Subcooling and Superheat are high,
adjust
the
TXV valve to the superheat specified in the table
below then check the Subcooling value.
d. If Subcooling is high and Superheat is low,
adjust
the TXV valve to the superheat specified in the
table below and
remove
charge to lower the
Subcooling to 8°F +/- 1°F.
NOTE: DO NOT
adjust the charge based exclusively
on suction pressure unless for general charging
in the case of a gross undercharge.
NOTE: Check the Schrader ports for leaks and
tighten valve cores if necessary. Install caps
finger-tight.
