TM 9-4120-371-14
a. Inspection
(1) Inspect for evidence of leaks, kinked, or otherwise damaged capillary line, and loose or missing
mounting hardware.
(2) Check thermal bulb to see that it is securely clamped to the suction line.
If a leak is suspected or indicated, test per paragraph 59.
(3)
b. Testing and superheat adjustment. The expansion valve as supplied with the unit is preset at the factory.
This valve should not be adjusted unnecessarily.
(1)
Perform a refrigerant pressure check on unit in accordance with paragraph 512. Leave gages or
service manifold attached.
(2) Remove the suction line insulation from the area of the sensing bulb. Observe location and
position of bulb for reinstallation.
(3) Loosen the screws and nuts in the bulb straps that attach the sensing bulb to the suction line, and
pull the bulb out of the straps.
Use care to not damage or kink the capillary.
The following test must be conducted with the power on. Exercise extreme caution.
(4)
Place the sensing bulb in a container of ice water or crushed ice so that it is reduced to a
temperature near 32F (0C).
(5) Set the Temperature control thermostat knob fully DECREASE (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 0.14
kg/cm2). If the pressure is not within the above limits, test the operation of the quench valve (para 5-16) and
the pressure regulator valve (para 5-24) before attempting adjustment of the evaporator expansion valve.
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
floodback 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.
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