TM 9-4120-357-14
e. With power connected to the air conditioner, turn the mode selector switch to COOL, and turn the temperature
control thermostat to maximum DECREASE Position. With compressor operating, observe the sight glass liquid indi-
cator. If bubbles or milkiness appear, top off the refrigerant charge as follows:
1. Connect a cylinder of refrigerant, R22, loosely to the gage port of the suction line service valve, and open the
cylinder shutoff valve for a few seconds to purge air from the line. Tighten the connection. Leave the cylinder up-right.
2.
With the air conditioner compressor operating, open the suction line service valve and the cylinder shutoff valve
to charge refrigerant gas into the system, while observing the sight-glass liquid indicator.
3. When the liquid in the sight-glass indicator runs clear and free of bubbles, close the suction line service valve and
the cylinder shutoff valve.
4. Disconnect the refrigerant cylinder, and replace caps on both service valves.
g. Final Assembly. Install panels and grilles on the air conditioner in accordance with the following steps:
(1) Position the two evaporator intake grilles on
the front of
the air conditioner, and secure with 12
screws and
washers in each.
(2) Place the lower edge of the front access panel behind the step in the base plate, and push into contact with the
air conditioner casing. Secure with four panel fastener screws.
5-26. Thermal Expansion Valves.
Two thermal expansion valves are used in the refrigeration system: one which meters refrigerant to the evaporator coil
(V5) and the other which injects liquid refrigerant into the compressor suction line (V4) . (See Figure 1-5.) Both valves
respond to temperature changes in the refrigerant line to which their remote bulbs are attached. The effects of pressure-
drop across the evaporator coil are canceled by a pressure equalization line from the evaporator thermal expansion
valve (V5) to the downstream (suction) end of the evaporator coil just beyond the sensing bulb. This pressure equaliza-
tion permits the valve to respond more quickly to temperature variations alone. Since pressure-drop in the liquid injec-
tion circuit is insignificant, valve V4 is equalized internally. Both valves are hermetically sealed to their sensing bulbs
a. Access. Obtain access to the thermal expansion valves as indicated below:
(1) Evaporator Expansion Valve. Obtain access to the evaporator expansion valve and its associated sensing
bulb in accordance with the following steps:
(a) Remove 31 screws and washers from the top panel. Remove the top panel.
(b) Remove 12
screws and washers from each of
the two evaporator intake grilles. Remove the grilles.
(2) Liquid Injection Expansion Valve. Gain access to the liquid injection expansion valve by unscrewing four
panel fastener screws that secure the front access panel. Remove the panel.
b. Testing. Both expansion valves are tested in the same manner, as follows:
(1) Stop the air conditioner. Let the suction line warm up to ambient temperature.
(2) Remove the sensing bulb from its location against the suction line, and place it in a container of ice water or
crushed ice (32F or 0C) .
CAUTION
Do not let liquid refrigerant flood back into the compressor longer than 1-2 seconds. The
expansion valve will be wide open during the following procedure. An excessive flood-
back of liquid refrigerant will damage the compressor.
(3) Start the air conditioner by setting the selector switch to cool, and the temperature control thermostat to de-
crease. Remove the sensing bulb from the ice water and hold it in one hand to warm it while feeling the suction line. If
the suction line temperature drops, the valve is operating properly. Stop the air conditioner at once, and re-install the
sensing bulb. If the temperature of the suction line does not drop, stop the air conditioner and replace the expansion
valve.
5-50