DIRECT SUPPORT TROUBLESHOOTING INTRODUCTION - CONTINUED
(g) A blockage at the outlet of the A/C receiver/dryer will cause low system high side pressure and little
or no cooling.
(h) If the A/C expansion valve is stuck closed, the A/C expansion valve and A/C evaporator coil will be at
(i) If the A/C expansion valve is stuck open, the A/C expansion valve and A/C evaporator coil will be
extremely cold and frost or ice buildup may occur.
(j) If ice is forming in the A/C expansion valve, the system may stop cooling when the ice forms, and
start cooling when the expansion valve warms up enough to melt the ice formed in the A/C expansion
valve, causing the system to appear to cycle ON and OFF.
(k) A blockage in the A/C evaporator coil will cause low system low side pressure and little or no cooling.
(l) A leak in the A/C evaporator or A/C expansion valve fittings may not be detectable with leak detector.
(m) A restriction in a low system side A/C hose will cause low system low side pressure and little or no
cooling. Cool spots and frost may form at location of restriction.
(n) A restriction in a high system side A/C hose will cause high system high side and low system low side
pressure and insufficient cooling. Cool spots and frost may form at location of restriction.
A/C system pressure checks. In addition to the performance checks noted above, the troubleshooting pro-
cedures for the HET Tractor A/C system will also include system pressure checks, using a standard A/C
manifold gage set. Before using the manifold gage set to measure A/C system pressure. Ensure that the
system is fully charged and stabilized. Stabilize the system by ensuring that all cab windows and vents are
closed, personnel heater is OFF, and running the system at high A/C blower speed for 5 to 10 minutes.
Wire Repair. Refer to TM 9-2320-360-20 for the repair of wire harness connectors. Refer to TM 43-0158 for
detailed instructions concerning electrical wiring repairs. If a wire harness cannot be repaired, replace the defective
A/C System Leak Repair. The majority of all A/C services will consist of locating and repairing A/C system
leaks. Many leaks will be located at points of connections, and are caused by vibration. Occasionally an A/C hose
will rub on a structural part or deteriorate, creating a leak. Or an A/C system component will develop a leak. These
leaks can be repaired in the following manner.
Minor leaks at connectors. Most minor leaks at connectors can be repaired by tightening the connectors or
replacing the O-ring. Use two wrenches when loosening or tightening connectors to avoid strain on A/C
hoses. Recover refrigerant before tightening connectors or replacing O-ring. See work package WP 0056
00 for refrigerant recovery.
Defective A/C hoses. Damaged or deteriorated A/C hoses must be replaced. See work package WP 0052
00 for A/C hose replacement.
A/C component leaks. If an A/C component develops a leak, which can not be repaired by tightening fit-
tings or replacing O-ring, the component may have to be replaced. See the associated work package for
Whenever repairs are made to any A/C part that holds refrigerant, you must recover, purge or flush (if con-
taminated), evacuate, charge, and leak test the system. In a good system, refrigerant lines are always under
pressure and you should disconnect them only after the refrigerant has been recovered with refrigerant
recovery unit through service valves (WP 0056 00).
WAR N I N G
Use care to prevent refrigerant from touching your skin or eyes. Liquid refrigerant, when exposed to the air,
quickly evaporates and will freeze skin or eye tissue. Serious injury or blindness may result if you come in
contact with liquid refrigerant.