TM 9-4120-399-14
it should indicate approximately 58 2 psig (4.0 kg/cm2). If the pressure is not within the
above limits, test the operation of the quench valve (para. 5-21) and the pressure regulating valve
CAUTION
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. 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.
(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.
5-53
