TM 9-2320-302-34
0009 00-1
AIR CONDITIONING SYSTEM TROUBLESHOOTING AND TESTING
0009 00
PRELIMINARY CHECKS
Before testing the operation of the air conditioning system, make the following checks:
1.
Ensure the refrigerant compressor’s drive belt is not damaged and is correctly tensioned. Also check the compressor
mountings for tightness.
2.
Check for broken, burst or cut hoses; also check for loose fittings on all parts.
3.
Check for road debris buildup on the condenser coil fins. Using air pressure and a whiskbroom or a soapy spray of
water, carefully clean off the condenser; be careful not to bend the fins.
4.
Check the color of the moisture indicator sight glass. If the color is a deep cobalt blue, the refrigerant charge is dry. If
the indicator is not blue, the system is contaminated with moisture. Recover the refrigerant, evacuate the system, replace
the receiver-drier, and add a full refrigerant charge (WP 0112 00).
5.
If there is not enough airflow, ensure leaves or other debris have not entered the fresh air ports under the windshield. If
debris has entered, it could clog the fins of the evaporator core, and block airflow. Also, be sure that all ducts are con-
nected to the dash louvers and that the air-control flaps in the heater housing are moving properly (this requires removal
of the right and center dash panel).
PERFORMANCE TESTS
Following is a brief description of symptoms or conditions that could exist if something goes wrong with a refrigerant
part.
1.
Receiver-Drier.
a.
The receiver-drier is normally at outside temperature. To the touch, the entire length of the unit should be the same
temperature. If noticeable cool spots exist, replace receiver-drier (WP 0118 00).
b.
A blockage at the inlet of the unit will cause high head pressures; outlet blockages will cause low head pressures
and little or no cooling.
c.
If the moisture indicator is pink or white (showing that the system is wet), the receiver-drier is saturated with mois-
ture and must be replaced (WP 0118 00).
2.
Cooling System.
a.
Although they are not physically connected, there is a close tie between vehicle’s air conditioner and cooling sys-
tem. Poor air conditioner cooling can be the result of a problem in the cooling system.
b.
If the cooling system does not work correctly, the heat of the engine will rise to abnormal levels. The added heat
will transfer to the air conditioner, other underhood parts, and may make its way into the cab. The added heat
makes it necessary for the air conditioner to work harder and, at the same time, it reduces the air conditioner’s abil-
ity to cool down the air in the cab. Also, if the water regulating valve isn’t closing all the way, heat will enter the
cab, giving the impression that the air conditioning system is not working.
c.
Refer to TM 9-2320-302-20 to troubleshoot engine cooling system.
3.
Expansion Valve.
a.
Problems that start in the expansion valve show up as follows: when stuck closed, the evaporator coil and the
expansion valve will be at outside temperature; when stuck open, both the coil and the valve will be extremely cold
with frost or ice buildup.
b.
Because the expansion valve channels are very small, blockages in the system tend to be found here (the valve is
very sensitive to contamination). Usually, the contaminant is water; less than a drop of water is all it takes to make
the valve inoperative. When water reaches the valve, the extreme cold that results from the pressure drop freezes
the water, forming a block of ice in the valve. After the system shuts down and the valve warms up, the ice melts,
and the valve operates again, only to freeze up when the moisture returns.
c.
On-and-off operation of the expansion valve means that the receiver-drier is not removing moisture from the sys-
tem. These contaminants should cause the moisture indicator’s element to turn white and then pink.
