TM 9-4120-357-14
5-16.
Replacement of Pressure Cutoff Switches.
a. Access to Switches. Dismantle the air conditioner to the extent necessary to remove the high and low pressure
cutoff switches in accordance with the following procedures:
(1) Unscrew four panel fastener screws from the front access panel, and remove the panel.
(2) Connect a hose to the gage port of the suction service valve, and crack the valve open to discharge refrigerant
gas over a period of 5-6 hours. Too rapid discharge will cause oil to be blown out of the system. Use a hose of sufficient
length to conduct the refrigerant gas to a safe area.
WARNING
Disconnect power from the air conditioner before performing main-
tenance on the electrical system. The voltage used can be lethal.
(3) Disconnect plug, P2, from the condenser fan motor, and disconnect plug (P16) from the top of
the pressure
CAUTION
Do not disconnect capillary tubes or pressure tube connections
until refrigerant is completely discharged from system.
(4) Unscrew flare nuts from the connections of both capillary tubes, and carefully coil capillary tubes up to the
pressure cutout switch housing (7).
(5) Remove the four screws above and below the cutout switch reset buttons while an assistant holds the switch
housing from inside the casing. Remove the housing, switches, and attached capillary tubes.
b. Removal. Remove four screws and lock washers from the bottom of the housing (7).
Press out grommet (8)
and carefully remove both pressure cutout switch assemblies. Pry off the metal retainer clip (3) from the top, remove the
insulating cover (2) and unscrew electrical terminal screws to disconnect the wiring harness (6) and wire lead (5).
c. Testing.
CAUTION
Do not use compressed air for pressure testing refrigeration com-
ponents. It contains traces of oil and moisture which can contami-
nate the refrigerant.
(1) Connect a
cylinder of
dry nitrogen and a
0-500 PSI. (0.35 KG/CM2) pressure gage to
the high-pressure cutout
switch capillary tubes.
(2) Connect an
ohmmeter or
continuity tester across the terminals of
the high-pressure cutout switch.
(3) Slowly apply pressure to the tube connection. When pressure reaches 415 PSIG, (29.2 KG/CM2) press reset
(4) Continue applying pressure to
the tube connection. Continuity should drop out at
460+ 10
PSIG (32.3 +
KG/CM2). If continuity requirements are not met, replace the high-pressure cutout switch.
(5) Transfer the dry nitrogen and ohmmeter or
continuity tester to
the low-pressure cutout switch.
(6) Slowly apply pressure to the tube connection. When pressure reaches 20 + 5 PSIG (1.4 + 0.35 KG/CM2),
press reset button. Continuity should be indicated.
(7) Reduce pressure slowly. Continuity should drop out at 7 + 5
PSIG (0.49 +
0.35 KG/CM2). If
continuity re-
quirements are not met, replace the low-pressure cutout switch.
d. Assembly. With the insulating covers removed from both pressure cutout switches assemble as follows:
(1) Facing the reset button sides of
the pressure cutout switches, place the high-pressure switch (1, Figure 5-3) on
the right-hand side of the low-pressure switch (4), and connect electrical lead (5, Figure 5-2) from terminal 1 of high-
pressure cutout switch (1) to terminal 2 of switch (4).
5-19