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TM 9-4120-389-14
(5)
Set the temperature control thermostat knob to fully COOLER (counter clockwise), place one
hand on the exposed suction return line, and start the air conditioner in COOL mode. If a drop in temperature
is felt on the suction return line, the expansion valve is not closing fully and should be replaced. If the return
line temperature remains constant, check the pressure gage; it should indicate approximately 58 ± 2 psi (4.0 +
kg/cm2). If the pressure is not within the above limits, ,test the operation of the quench valve (para. 5-17) and
the hot gas bypass valve (para. 5-18).
CAUTION
When performing the next test, turn the air conditioner to OFF as soon as a
definite drop in temperature is felt on the suction return line. If the test conditions
are continued more than a few seconds, the expansion valve will fully open and an
excessive flood-back of liquid refrigerant may damage or destroy the compressor.
(6)
With one hand still on the suction return line, remove the sensing bulb from the container and
warm it in the other palm. If a temperature drop is not felt in the suction return line by the time the sensing bulb
no longer feels cold to the hand, the expansion valve is not opening and should be replaced. As soon as a
temperature drop is felt, turn the air conditioner to OFF.
NOTE
The optimum superheat setting for the evaporator expansion valve is 12 deg. F
(35 psig) above the saturation temperature of the refrigerant at operating suction
line pressure. This setting will provide maximum efficiency of the evaporator coil.
5-57
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