Carrier 69NT40-541-306, Operation And Service

Page: 110 / 154

T-354 7–22
5. 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 5 or 6 readings
6. From the temperature/pressure chart ( Table 7–8 ), determine the saturation temperature corresponding to
the evaporator outlet test pressures at the suction modulation valve.
7. Subtract the saturation temperatures determined in step f from the temperatures measured in step e.
8. The difference 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 Expansion Valve Replacement
Removing the Expansion Valve
NOTES
1. The TXV is a hermetic valve and does not have adjustable superheat (See Figure 7.20 ).
2. All connections on the hermetic TXV are bi-metallic, copper on the inside and stainless on the outside.
3. All joints on the hermetic TXV (inlet, outlet and equalizer lines) are brazed.
4. Bi-metallic connections heat up very quickly.
Figure 7.20 Thermostatic Expansion Valve
1. Hermetic Thermostatic Expansion Valve (TXV)
2. Non-adjustable Superheat Stem
3. Equalizer Connection 4. Inlet Connection
5. Outlet Connection
6. Hermetic Expansion Valve Bulb
- - - - -
Figure 7.21 Hermetic Thermostatic Expansion Valve Brazing Procedure
1
2
3
4
5
6
Copper Tube
(Apply heat for 10-15 seconds)
Bi-metallic Tube Connection
(Apply heat for 2-5 seconds)
Use of a wet cloth is not necessary due to rapid
heat dissipation of the bi-metallic connections
Braze Rod (’Sil-Phos” = 5.5% Silver, 6% Phosphorus)