6-14
T--317
1. Pump down the unit and replace filter-drier.
2. Evacuate the system in accordance with paragraph
6.6.
3. After unit is in operation, inspect for moisture in sys-
tem and check charge.
6.14 THERMOSTATIC EXPANSION VALVE
The thermal expansion valve (see Figure 2-2) is an
automatic device which maintains constant superheat
of the refrigerant gas leaving the evaporator, regardless
of suction pressure.
The valve functions are:
1. Automatic control of the refrigerant flow to match the
evaporator load.
2. Prevention of liquid refrigerant entering the com-
pressor.
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 6-18.) On units fitted with a semi--hermetic valve,
check to be sure the excess capillary is secured to the
power head assembly and wrapped with insulating
compound.
1
2
3
4
1. Suction Line
2. TXV Bulb Clamp
3. Nut and Bolt
4. TXV Bulb
Figure 6-18 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 2-1) to ex-
pose 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 6-9), de-
termine the saturation temperature corresponding to
the evaporator outlet test pressures at the suction
modulation valve.
g. Subtract the saturation temperatures determined in
step f. from the temperatures measured in step e..
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)
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 6-19 Hermetic Thermostatic Expansion Valve Brazing Procedure
Содержание 69NT40--541--200 TO 299
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