TM 9-4120-404-14
- Continued.
4-26. EXPANSION VALVE.
CAUTION
Damage to the capillary tube will cause the unit to malfunction. Use care not to
damage or kink the capillary.
NOTE
If air conditioner cycles on and off during expansion valve testing, pull coil frost
switch sensor out of the evaporator coil and manually control thermistor to
maintain unit operation.
(6) Place the sens ing bulb (1) in a container of ice water or crushed ice so that it is reduced to a temperature of
32 F (0 C) and a gauge reading of 41 psi.
(7) Remove sensing bulb from ice water and check that gauge reading quickly increases.
(8) If gauge readings on either test are incorrect, replace expansion 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.
NOTE
The expansion valve as supplied with the unit is preset at the factory. This valve
cannot be adjusted. The factory set superheat setting for the expansion valve is
12F(35 psig) above the saturation temperature of the refrigerant at operating
suction line pressure. This setting will provide maximum efficiency of the
evaporator coil.
(1) Remove two screws (7), two lock washers (8), and block off plate (9).
(2) Restrain expansion valve (10).
(3) Debraze tubing attached to expansion valve (10) (see para. 4-7).
(4) Unwrap existing suction line insulation from around sensing bulb (1) and remove expansion valve (10) from
unit.
4-60
