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9. Attach the sensor bulb just below center of the
suction line (4 or 7 o'clock position viewing
from cross section to the suction line, see
Figure 4-8). This area must be clean to ensure
positive bulb contact. Do not insulate the bulb
until the superheat is measured.
10. Fasten equalizer tube to expansion valve,
using oil on flare connections.
11. Connect vacuum pump to the compressor
suction service valve
evacuate to 500 microns. Isolate pump from
system.
12. Open the inlet service valve to the filter-drier.
Check refrigerant level. (Refer to sections 4.5
and 4.9.)
13. Check superheat.
1
7
8
Figure 4-7. Thermostatic Expansion Valve
b. To Measure Superheat
When conducting this test the suction
pressure must be at least 6 psig (0.42
kg/cm@) below the
maximum operating pressure (MOP).
Refer to section 1.2.d for applicable valve
settings.
1. Remove insulation from sensor bulb and
suction line if installed.
2. Loosen one bulb clamp and make sure area
under clamp is clean.
3. Place the temperature thermocouple above
(parallel) TXV bulb and tighten loosened
clamp making sure both bulbs are firmly
secured to suction line as shown in Figure 4-8.
service
port and
2
3
1. Power Head
Assembly
4
2. Equalizer
Connection
3. Sensor Bulb
5
4. Cage Assembly
5. Seat Gasket
6
6. Body Flange
7. Capscrew
8. Body Flange
7
Gaskets
NOTE
expansion valve
Place insulation around TXV bulb and
thermocouple.
4. Connect suction gauge to the service port on
the compressor suction service valve.
5. Set temperature selector to lowest setting.
Run unit for at least 20 minutes to stabilize the
system.
6. Using
the
(Table 4-2) for the applicable refrigerant used,
determine
the
corresponding to the pressure taken at the
suction service valve.
7. Note the temperature of the suction gas at the
sensor bulb.
8. Subtract
the
determined in Step 6 from the average
temperature measured in Step 7. The
difference is the superheat of the suction gas.
Figure 4-8. Thermostatic Expansion Valve Bulb
and Thermocouple
c. Superheat Adjustment
The thermostatic expansion valves used in this
application are not adjustable. The valve is preset
at the factory and should not require adjustment.
4.13 REMOVING THE HEATER COIL
a. Disconnect the bus battery.
b. Remove evaporator motor and heater coil
access panels.
c. Open the air vent fitting at the top of the outlet
header of the heater coil to bleed.
d. Open the drain-cock on the coolant inlet tube
to drain coil.
e. Remove
both
assemblies with mounting brackets (refer to
section 4.16).
f.
Disconnect hoses from the coil.
g. Disconnect and remove coolant solenoid valve
assembly from the unit.
4-9
temperature/pressure
saturation
temperature
saturation
temperature
1
1. Suction Line
(end view)
2
2. Clamp
3. Thermocouple
3
4. TXV Sensor Bulb
4
evaporator
fan
chart
motor
T-288
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