9
Fixed Orifice
1. Temporarily install a thermometer 4-6" from the compres-
sor on the suction line. Ensure the thermometer makes
adequate contact and is insulated for best possible read-
ings. Use vapor temperature to determine superheat.
2. Refer to the superheat table provided for proper system
superheat. Add charge to lower superheat or recover
charge to raise superheat.
Expansion Valve System
NOTE: Units matched with indoor coils equipped with a
non-adjustable TXV should be charged by Subcooling only.
SUBCOOLING FORMULA = SATURATED LIQUID LINE TEM-
PERATURE - LIQUID LINE TEMPERATURE
1. Purge the gauge lines and connect the service gauge
manifold to the base valve service ports.
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 con-
densing 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 re-
frigerant 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, differ-
ences in height between the indoor and outdoor unit and
refrigerant tubing sizes. These adjustments should only
be performed by qualified service personnel.
Advanced Adjustment Recommendations
SUPERHEAT FORMULA = SUCTION LINE TEMPERA-
TURE - SATURATED SUCTION TEMPERATURE
1. Clamp a pipe clamp thermometer near the suction line
service valve at the outdoor unit.
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 Su-
perheat value.
3. TXV-based systems should have a Superheat value of
8
°
F +/- 1
°
F.
4. Adjust Superheat by turning the TXV valve stem
clock-
wise
to
increase
and
counterclockwise
to
decrease
.
a. If Subcooling and Superheat are low,
adjust
the TXV
to 8
°
F +/- 1
°
F, 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 Super-
heat.
c. If Subcooling and Superheat are high,
adjust
the TXV
valve to 8
°
F +/- 1
°
F Superheat, then check the
Subcooling value.
d. If Subcooling is high and Superheat is low,
adjust
the TXV valve to 8
°
F +/- 1
°
F Superheat 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.
Heat Pump - Heating Cycle
The proper method of charging a heat pump in the heat mode
is by weight with the additional charge adjustments for line
size, line length, and other system components. For best
results, on outdoor units with TXVs, superheat should be 5
°
F
+/- 1
°
F at 4-6" from the compressor. Make final charge adjust-
ments in the cooling cycle.