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4-8
7. Note the temperature of the suction gas at the
sensor bulb.
8. Subtract the saturation temperature determined
in Step 6 from the average temperature measured in Step
7. The difference is the superheat of the suction gas.
1. Suction Line
(end view)
2. Clamp
3. Thermocouple
4. TXV Sensor Bulb
1
2
3
4
Figure 4-8. Thermostatic Expansion Valve Bulb
and Thermocouple
c. Adjusting Superheat
Refer to section 1.2.c for the superheat setting.
The thermostatic expansion valve used in this
application is externally adjustable. The valve is preset at
the factory and should not be adjusted unnecessarily. If
necessary to adjust the superheat, proceed as follows:
1. Remove the seal cap to gain access to the
superheat adjusting stem (see Figure 4-7).
2. Turn the adjusting stem clockwise to compress the
valve spring which will decrease refrigerant flow through
the valve, increasing superheat. Turn the adjusting stem
counterclockwise to decompress the valve spring which
will increase refrigerant flow through the valve,
decreasing superheat.
3. When the unit has stabilized operation for at least
20 minutes, recheck superheat setting.
4. If superheat setting is correct, replace stem cap,
remove gauge and thermocouple. Insulate bulb and
suction line.
4.13 REMOVING THE HEATER COIL
a. Place the run control switch in the “OFF”
position.
b. Open the air vent fitting at the top of the outlet
header of the heater coil to bleed.
c. Drain coil by removing enough coolant from
vehicle cooling system.
d. Disconnect water line from the coil.
CAUTION
If unit was recently operating, be careful of
remaining hot coolant in the hoses when
disassembling.
e. Remove coil retaining bolts on each side of the coil
assembly (two each side). Pull top of coil assembly up and
out to remove from unit.
f. Reverse procedure for installing new heater coil
assembly.
4.14 REPLACEMENT OF EVAPORATOR COIL
a. If refrigerant remains in the system, perform a low
side pump down, removing all refrigerant from the
evaporator coils.
b. Using a 1/4’’ allen wrench, remove the three allen
head bolts (1 bolt on the back end, and 2 on the front
end)securing the heater coil to the evaporator coil that is
to be removed.
c. Remove the TXV power head assembly and the
TXV support bracket from the body of the TXV.
d. Remove the two bolts on the back end of the
evaporate coil, securing the evaporator coil. to the
evaporate sub-frame. From the inside of the coach,
reaching up through return air opening, remove the two
bolts at the front end of the evaporator coil securing it to
the sub-frame.
e. The panel covering the evaporate coil needs to be
removed by loosening the phillips head screws along the
overlapped edge of the control panel.
f. The brazed inlet and outlet lines need to be
unsolder, but caution must be taken with the flame of the
brazing torch so that no damage is done to the unit’s
fiberglass shell.
g. Once the inlet and outlet lines are loose the
evaporate coil can be lifted up and out of the unit.
h. To install replacement evaporate coil reverse the
above procedure.