Figure 4--12 Thermostatic Expansion Valve; Figure 4--13 Thermostatic Expansion Valve Bulb And Thermocouple; Table - Carrier EM-17 Operation And Service

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1. Power Head
Assembly
2. Equalizer Connection
3. Bulb
Figure 4- -12 Thermostatic Expansion Valve
4.13.1 Valve Replacement
a. Pump down low side of the unit. Refer to paragraph
4.4.1.
b. Remove insulation from expansion valve and bulb.
See Figure 4--12 and Figure 4--13.
c. Loosen retaining straps holding bulb to suction line
and detach bulb from the suction line.
d. Loosen flare nuts on equalizer line and disconnect
equalizer line from the expansion valve.
e. Remove capscrews and lift off power head and cage
assemblies and gaskets.
f. Check, clean and remove any foreign material from
the valve body, valve seat and mating surfaces. If re-
quired, replace valve body.
NOTE
R-134a valves are non-adjustable.
g. Using new gaskets, install new cage and power head
assemblies.
h. Fasten equalizer line to the expansion valve.
i. Leak check the new valve and evacuate and dehy-
drate low side. Refer to paragraph 4.4.1.
j. The thermal bulb is installed below the center of the
suction line (four or eight o'clock position). This area
must be clean to ensure positive bulb contact. Strap
thermal bulb to suction line. Ensure that retaining
straps are tight and renew insulation.
k. If required, add vapor refrigerant to bring low side
pressure to 20 to 30 PSIG (R-134a). Open filter-drier
inlet service valve and compressor service valves.
l. Run the coach for approximately 30 minutes on fast
idle.
m.Check refrigerant level. Refer to paragraph 4.7.1.
n. Check superheat. Refer to paragraph 4.13.2.
T-336
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3
4
5
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6
7
4. Gasket
5. Cage Assembly
6. Body Flange
7. Cap screw
4--10
4.13.2 Superheat Measurement
NOTE
All readings must be taken from the TXV bulb
location and out of the direct air stream.
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2
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1. Suction Line
(section view)
2. TXV Bulb Clamp
3. Nut & Bolt (clamp)
Figure 4- -13 Thermostatic Expansion Valve Bulb
and Thermocouple
a. Remove Presstite insulation from expansion valve
bulb and suction line.
b. Loosen one TXV bulb clamp and make sure area un-
der clamp is clean.
c. Place temperature thermocouple in contact with the
suction tube and parallel to the TXV bulb, and then
secure loosened clamp making sure both bulb and
thermocouple are firmly secured to suction line. See
Figure 4--13. Reinstall insulation around the bulb.
d. Connect an accurate low pressure gauge to the low
pressure port (Figure 1--5).
e. Start bus and run on fast idle until unit has stabilized,
about 20 to 30 minutes.
NOTE
When conducting this test, the suction pressure
must be at least 6 psig (0.41 bar) below the ex-
pansion valve maximum operating pressure
(MOP). Refer to paragraph NO TAG for MOP.
f. From the temperature/pressure chart (Table 4--2),
determine the saturation temperature corresponding
to the evaporator outlet pressure.
g. Note the temperature of the suction gas at the expan-
sion valve bulb. Subtract the saturation temperature
from this temperature. The difference is the super-
heat of the suction gas.
h. The superheat may cycle from a low to high reading.
Monitor the superheat taking readings every 3-5 min-
utes for a total of 5-6 readings. Calculate the super-
heats, add the readings and divide by the number of
readings taken to determine average superheat. Re-
fer to paragraph NO TAG for superheat setting.
i. If superheat is not within tolerance, replace the valve.
4.14 REPLACING RETURN AIR FILTERS
The return air filters are located behind the return air
grill, inside the vehicle.
The filters should be checked for cleanliness
periodically depending on operating conditions. A dirty
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5
4. Thermocouple
5. TXV Bulb (Shown
in the 4'clock
position)
05/09