TM 9-4120-407-14
4-29. EXPANSION VALVE TESTING AND REPLACEMENT. (Cont)
(2) Open a portion of insulation (1) and attach an accurate thermometer to tubing (2) near the sensing
bulb (3). Close the insulation and wrap with insulation tape.
(4) Operate the air conditioner in the COOL mode with the TEMPERATURE control set fully to
COOL position per paragraph 2-7. Allow the air conditioner to run until the thermometer and
suction pressure readings remain unchanged for at least 2 minutes.
(5) Note the pressure on the suction gauge. Find the saturation temperature for the suction pressure
per Table 4-1 and compare this temperature to the thermometer temperature. The thermometer
temperature should be 10 + 1 F (5.55 + 0.55 C) higher than the saturation temperature. This is
the superheat temperature for the air conditioner.
(6) If the superheat temperature is not within tolerance, adjust the expansion valve (6) as follows:
(a) Remove cap (19).
(b) Turning the adjusting stem (20) two complete turns will change the superheat setting 1 F
(0.55 C). Turn the stem clockwise to increase the superheat and counterclockwise to decrease
it. Turn only two full turns, then wait for the thermometer temperature and suction pressure to
stabilize. Check superheat before making another adjustment.
(c) If the superheat cannot be adjusted to within tolerance, the expansion valve (6) must be
replaced.
(d) Install cap (19).
(8) Remove the thermometer and wrap insulation (1) with insulation tape as necessary to seal it.
NOTE
FOLLOW-ON MAINTENANCE:
4-68