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TM 5-4120-270-15
(3) If valve fails to click closed, stop air
conditioner and test valve according to instructions in
paragraph 618.
c. Removal and Disassembly. Discharge refrigerant
system (para 6-28). Refer to figure 58 and remove and
disassemble the liquid line solenoid valve.
Caution: Do not remove tubing from valve to
avoid heat distortion of integral parts.
d. Reassembly and Installation. Replace any
defective parts. Reassemble valve and install in reverse
order of removal as illustrated on figure 5-8. Test,
evacuate and recharge the refrigerant system (para 6-
28, 29, 30).
6-20. Back Pressure Regulating Valve
a. General. The back pressure regulating valve (fig.
5-9), regulates refrigerant pressure in the evaporator to
prevent coil freeze up. Valve is preset to establish a
minimum pressure of 57.8 psig in the evaporator. The
back pressure regulating valve also bypasses refrigerant
gas from the discharge line to the suction line during
bypass operation with the selector switch on "COOL".
b. Adjusting. Remove button plug from the back
pressure regulating valve, (fig. 5-9), loosen the lock nut
at the top of the valve and turn the adjusting screw.
Tighten the lock nut after adjustment and check system
operating pressures (para 6-14).
c. Removal. Refer to figure 5-9, and remove the
back pressure regulator valve.
Note. Discharge the refrigerant before removing
back pressure valve.
d. Installation. Replace a defective back pressure
regulating valve and install in reversing order of removal
as illustrated on figure 5-9. Test, evacuate and recharge
refrigerant system (para 6-28, 29, 30).
6-21. High and Low Pressure Cutout Switches
a. General. The high pressure cutout switch
prevents the compressor from operating if the head
pressure exceeds 445 psig (pounds per square inch
gage). The low pressure cutout switch prevents the
compressor from operating if the suction line pressure
drops below 7 psig.
b. Removal. Discharge the refrigerant system and
remove high and low pressure cutout switches as
illustrated in figure 5-10.
c. Testing. Test the pressure switches for continuity
across the connector pins with a multimeter set on
OHMS. If no continuity is indicated, press the reset
button and recheck.
d. Installation. Replace defective pressure cutout
switches in reverse order of removal as illustrated in
figure 5-10. Test, evacuate and recharge the unit
refrigerant system (para 6-28, 29, 30).
6-22. Pressure Relief Valve
a. General. The pressure relief valve (fig. 5-12) is
located on a cross just above the dehydrator. The
pressure relief valve protects the refrigerant system from
excessive pressure. It is preset to open at a maximum
pressure of 540 psig and is not adjustable.
b. Removal. Discharge the refrigerant system, refer
to figure 5-12, and remove the pressure relief valve.
c. Installation. Replace a defective pressure relief
valve by reversing order of removal as illustrated on
figure 5-12. Pressure test, evacuate and recharge
refrigerating system (para 6-28, 29, 30).
6-23. Evaporator Coil
a. General. The evaporator coil is mounted on the
casing, directly behind the discharge grille. The coil must
be removed from the air conditioner for repair or
replacement. The coil is made of brazed aluminum and
is of the finned plate configuration.
b. Removal. Refer to figure 5-5 and remove
evaporator coil.
c. Cleaning, Inspection and Repair. Refer to
paragraph 3-10 and clean and inspect the evaporator coil
in a similar manner. Inspect coil for bent fins, damaged
coil runs and internal leaks. Straighten bent fins with
needle nose pliers. A damaged coil or an internally
leaking coil cannot be repaired.
d. Installation. Replace a defective evaporator coil
assembly and install in reverse order of removal as
illustrated in figure 5-5. Test, evacuate and recharge
refrigerating system (para 6-28, 29, 30).
6-24. Condenser Coil
a. General. The condenser coil is mounted
horizontally on the bottom third of the casing, beneath
the air filters. The coil must be removed from the air
conditioner for repair or replacement. The coil is made
from brazed aluminum and is of the finned plate
configuration.
b. Removal. Refer to figure 5-s3, and remove
condenser coil.
c. Cleaning, Inspection, and Repair. Refer to
paragraph 3-11 and clean and inspect the condenser coil
in a similar manner.
6-14
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