TM 9-4120-360-14
a. Remove the filter-drier, and blow down each leg of there frigeration system. To do this, connect a cylinder of
dry nitrogen to each filter-drier connection, in turn, and open the cylinder shutoff valve for at least 30 seconds at 50 psig
(3.5 kg/cm2) pressure.
b. Connect the two filter-drier fittings with a jumper locally manufactured from refrigerant tubing and fittings,
and install a pump. reservoir and filter in place of the compressor. (See figure 5-5).
c. Disassemble both expansion valves and temporarily remove the valve cages. Re-install shell of power
assembly, using a locally manufactured gasket between power assembly and body to prevent leakage. Tag and retain
valve cages for use at re-assembly.
NOTE
An unused filter-drier or other suitable medium may be used as the filter.
d. Fill reservoir with fluorocarbon refrigerant, R11, and start the pump. Continue filling the reservoir with
refrigerant, R11, until it begins to pour out of the return line. Continue flushing for at least 15 minutes.
NOTE
During flushing and back-flushing operations, apply 24 volts, dc, to the bypass line solenoid valve for a
total of approximately 10 minutes of each cycle. This will ensure that the cleaning solvent is forced through
all parts of the system.
e. Reverse the pump connections, replace the filter with a new filtering medium, and back-flush the systemfor
an additional 15 minutes.
f. Remove the pump, reservoir, filter and filter-drier jumper. Place an empty container below the compressor
connections, and connect a cylinder of dry nitrogen to each filter-drier connection in turn. Blow down each leg of the
system at 50 psig (3.5 kg/cm2) for at least 30 seconds.
g. Disassemble both expansion valves and re-install the valve cages. Install new gaskets, and assemble the
valves, making sure that projections on valve cages fit in notches in valve bodies.
h. Disconnect the dry nitrogen cylinder, and immediately install a new filter-drier, making sure that the
direction-of-flow arrow points up. Cap or plug compressor connections if compressor is not to be installed immediately.
Section V. PRESSURE SWITCH
5.31. Description
The pressure switch is a SPST switch which is connected in parallel with the manual two-speed fan switch on the control
panel. Its function is to connect power to the auxiliary windings of the two-speed fan motor when system pressure
increases to a preset point. The increased fan speed, and the resulting increase in airflow around both the condenser and
the evaporator coils has a tendency to decrease system pressure. which limits it to a safe and efficient level. Since the
pressure switch is connected in parallel with the manual two-speed fan switch it functions only when the manual switch is
set at LO SPEED and the air conditioner is operating in the cooling mode. The pressure switch is connected to the
refrigeration system at a tee fitting on the discharge side of the compressor. It closes at a pressure of 400 16 psi (28. 12
1.12 kg/cm2), and opens at a pressure of 350 16 psi (24.6 1.12 kg/cm2).
5.32. Removal
Remove the pressure switch from the air conditioner in accordance with the following directions:
a. Remove five screws from the frame of the fresh air damper screen, and remove the screen.
b. Refer to figure 5-8 for identification of service valves. Remove the cap from the suction service valve, and
discharge the system in accordance with paragraph 5.22.a.
