TM 9-4120-370-14
TO 35E9-229-1
5-22. EXPANSION VALVE - Continued.
(5) Set the Temperature control thermostat knob fully DECREASE (counterclockwise), 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
2
0.14 kg/cm ). If the pressure is not within the above limits, test the operation of the quench valve (para
427) and the pressure regulator valve (para 424) before attempting adjustment of
the evaporator expan-
sion valve.
CAUTION
When performing the next test, turn the air conditioner to OFF as soon as a defi-
nite 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 compres-
sor.
(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 Ilne 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 10F (5.55C)
above the saturation temperature of the refrigerant at operating suction line pressure.
This setting will provide maximum efficiency of the evaporator coil.
(7) Slip the sensing bulb into its mounting loop clamp. Be sure the bulb is installed in its original position and
tighten the nut and screw. Be sure the sensing bulb IS making metaltometal contact with the suction line.
(8) Attach an accurate thermometer to an exposed surface of the suction return line adjacent to the sensing
bulb: use a small glob of thermal mastic, if available, to improve conductivity.
(9) Rewrap insulation on the suction return line, being sure to cover the sensing bulb.
(10) Start the air conditioner in the COOL mode with the thermostat set at fully DECREASE (counterclockwise)
and allow it to run about 30 minutes, then check to be sure the temperature in the suction line has stabilized
and the thermometer reading remains unchanged for at least 2 minutes.
(11) Note the pressure on the gage connected to the low pressure (suction) service valve, Find the saturation
temperature for the pressure gage reading (See table 51.) and compare with the thermometer reading.
The thermometer temperature should be 10 1F (5.55 0.55C) higher than the saturation temperature
found on the chart.
(12) If the superheat setting is not within the limits shown above, adjust the expansion valve as follows:
(a) Remove the hexagonal seal cap from the side of the power assembly.
(b) Turn the adjusting stem two complete turns to change the superheat setting by 1F (0.55C). Turn
the stem clockwise to increase superheat span: counterclockwise to decrease it. Do not change more
than two full turns at one time, then wait at least 2 minutes for temperature to stabilize and recheck
pressure and temperature before further adjustment.
(13) When the proper setting is obtained.
(a) Turn unit OFF.
(b) Replace hexagonal seal cap.
(c) Remove thermometer.
(d) Cover the bulb and suction Ilne with two layers of insulation tape, item 12, Appendix E. Apply in spiral
with overlapping edges.
5-45