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 TM 5-4120-393-14
5-19. Expansion Valve (Primary) (cont)
NOTE
The optimum superheat setting for the evaporator expansion valve is 10 F (5.55 C)
above the saturation temperature of the refrigerant at operating suction line
pressure. This setting will provide maximum efficiency of the evaporator coil.
7.
Install the sensing bulb in its original position. Be sure the sensing bulb (3) is making metal to metal 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 amount of thermal mastic, if available, to improve conductivity.
9.
Rewrap insulation on suction return line being sure to cover 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 5-1) and compare with the thermometer reading. The thermometer
temperature should be 10 1F (5.55 0.55 C) 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 hexago nal seal cap (1) from the side of the power assembly (8).
b.
Turn the adjusting stem two complete turns to change the superheat setting by 1F (0.55 C). 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 (1).
c.
Remove thermometer.
d.
Cover the bulb and suction line with two layers of insulation tape, item 12 Appendix E.
Apply in spiral with
overlapping edges.
e.
Close service valves on unit.
f.
Remove gages or service manifold from service valves.
g.
Install valve stem and hose connection protective caps.
5-45
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