69
T-305
Unless the valve is defective, it seldom requires
maintenance other than periodic inspection to ensure
that the thermal bulb is tightly secured to the suction line
and wrapped with insulating compound. (See
Figure 40.)
1
2
3
4
1. Suction Line
2. TXV Bulb Clamp
3. Nut and Bolt
4. TXV Bulb
Figure 40. Thermostatic Expansion Valve Bulb
6.14.1 Checking Superheat.
NOTE
Proper superheat measurement should be
completed at --18
_
C (0
_
F) container box tem-
perature where possible.
a. Open the heater access panel (see Figure 1, page 5)
to expose the expansion valve .
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 direct-
ly 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 (Table 19,
page 84), determine the saturation temperature cor-
responding to the evaporator outlet test pressures at
the suction modulation valve.
g. Subtract the saturation temperatures determined in
step f. from the temperatures measured instep e. The
difference is the superheat of the suction gas. Deter-
mine the average superheat It should be 4.5 to 6.7
°
C
(8 to 12
°
F)
6.14.2 Hermetic Valve Replacement
a. Removing the Expansion Valve
NOTES
1. The TXV is a hermetic valve and does not
have adjustable superheat.
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.
1
2
3
4
5
6
1. Hermetic Thermostatic Expansion Valve
2. Non-adjustable Superheat Stem
3. Equalizer Connection
4. Inlet Connection
5. Outlet Connection
6. Hermetic Expansion Valve Bulb
Figure 41. Hermetic Thermostatic Expansion
Valve
1. Pump down the unit per section 6.4, page 59.
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 neces-
sary due to rapid heat dissipation
of the bi--metallic connections
Braze Rod
(’Sil-Phos” = 5.5% Silver, 6% Phosphorus)
Figure 42. Hermetic Thermostatic Expansion Valve Brazing Procedure
Содержание 69NT40-489-100 Series
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Страница 167: ...143 T 305 Based on drawings 62 10526 Rev and 62 10736 Rev Figure 90 Electrical Schematic CA...
Страница 168: ...144 T 305 ALTERNATE CONFIGURATION Figure 91 Electrical Wiring Diagram Controlled Atmosphere Sheet 1 of 2...
Страница 169: ...145 T 305 F Figure 88 E Figure 88 Figure 91 Electrical Wiring Diagram Controlled Atmosphere Sheet 2 of 2...
Страница 172: ...148 T 305 Figure 93 Electrical Wiring Diagram Sheet 1 of 2 Units not modified to include the N2 Purity Solenoid Valve...
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