9
7.4 Thermal Expansion Valve System Adjustment
The following information for the indoor unit should be
verified before attempting to charge system or adjust TXV if
necessary.
1. Total static pressure is .5” WC or less.
2.
Airflow is correct for installed unit.
3.
Airflow tables are in the installation manual and Spec
Sheet for Indoor Unit.
4.
Complete airflow tables and charging information are
in Service Manual RS6200006.
5. The outdoor temperature must be 60°F or higher.
6. Set the room thermostat to COOL, fan switch to AUTO
7. Set the temperature control well below room
temperature.
Superheat adjustments should not be made until indoor
ambient conditions have stabilized. This could take up to
24 hours depending on indoor temperature and humidity.
Before checking superheat run the unit in cooling for 10
minutes or until refrigerant pressures stabilize. Use the
following guidelines and methods to check unit operation
and ensure that the refrigerant charge is within limits.
NOTE: Charge two stage units on low stage.
1. Purge gauge lines. Connect service gauge manifold to
base-valve service ports.
2. 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
thermometer makes adequate contact and is insulated
for best possible readings. Use liquid line temperature
to determine subcooling and vapor temperature to
determine superheat.
3. Check subcooling and superheat. The system should
have a subcooling of 8°F +/- 1°F and two-stage
compressor systems should have a Subcooling of 6°F
+/- 1°F. and superheat of 8°F +/- 1°F. If subcooling
and superheat are low, adjust TXV to 8°F +/- 1°F
superheat, then check subcooling.
a. If subcooling is low and superheat is high,
add charge to raise subcooling to 8°F +/- 1°F.
Two-stage compressor systems should have a
Subcooling of 6°F +/- 1°F then check superheat.
b. If subcooling and superheat are high, adjust
TXV valve to 8°F +/- 1°F superheat, then check
subcooling.
Superheat Adjustments
(Only if necessary)
1. Attach 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.
2. TXV-based systems should have a Superheat value of
8°F +/- 1°F.
3. Adjust Superheat by turning the TXV valve stem
clockwise to increase and counterclockwise to
decrease. Adjustments should be made opening or
closing the valve by no more than ¼ turn at a time.
Allow the system to stabilize 15 to 20 minutes before
making additional adjustments if necessary.
4. After adjustments are complete replace cap on
adjustment stem and tighten 1/6 turn.
5. Remove gauges and check the Schrader ports for
leaks and tighten valve cores if necessary. Install caps
finger tight.
NOTE: In situations where the TXV must be removed
and replaced or re-installed into the system, the TXV
should be hand tightened first and then apply a half
turn to fully set the TXV. No more than 20 ft-lb torque
should be applied to the joints of the TXV.
SUCTION PRESSURE SATURATED SUCTION
PSIG
R-410A
50
1
52
3
54
4
56
6
58
7
60
8
62
10
64
11
66
13
68
14
70
15
72
16
74
17
76
19
78
20
80
21
85
24
90
26
95
29
100
31
110
36
120
41
130
45
140
49
150
53
160
56
170
60
SATURATED SUCTION PRESSURE
TEMPERATURE CHART
Table 5
SUBCOOL FORMULA =
SAT. LIQUID LINE TEMP. - LIQUID LINE TEMP.
SUPERHEAT FORMULA =
SUCT. LINE TEMP. - SAT. SUCT. TEMP.
