Checking Superheat; Hermetic Valve Replacement; Figure 7.20 Thermostatic Expansion Valve - Carrier 69NT40-541-001 Operation And Service

7.14.1

Checking Superheat.

Proper superheat measurement should be completed at -18°C (0°F) container box temperature
where possible.
a. Open the heater access panel (see
b. Attach a temperature sensor near the expansion valve bulb and insulate. Make sure the suction line is clean
and that firm contact is made with the sensor.
c. Connect an accurate gauge to the service port directly upstream of the suction modulating valve.
d. Set the temperature set point to -18°C (0°F), and run unit until conditions stabilize.
e. The readings may cycle from a high to a low reading. Take readings of temperature and pressure every
three to five minutes for a total of 5or 6 readings
f. From the temperature/pressure chart
the evaporator outlet test pressures at the suction modulation valve.
Subtract the saturation temperatures determined in step f. from the temperatures measured in step e. The differ-
ence is the superheat of the suction gas. Determine the average superheat. It should be 4.5 to 6.7°C (8 to 12°F).
7.14.2

Hermetic Valve Replacement

a. Removing the Expansion Valve
• The TXV is a hermetic valve and does not have adjustable superheat.
• All connections on the hermetic TXV are bi-metallic, copper on the inside and stainless on the outside.
• All joints on the hermetic TXV (inlet, outlet and equalizer lines) are brazed.
Bi-metallic connections heat up very quickly.
Hermetic Expansion
Valve Bulb
Outlet Connection
T-316
NOTE
Figure 3.1) to expose the expansion valve.
(Table 7–8), determine the saturation temperature corresponding to
NOTES

Figure 7.20 Thermostatic Expansion Valve

7–22
Hermetic Thermostatic
Expansion Valve
Non-adjustable Superheat Stem
Equalizer Connection
Inlet Connection