AIR CONDITIONING SYSTEM TESTS, INSPECTIONS, AND ADJUSTMENTS - CONTINUED
REFRIGERANT COMPRESSOR TEST
N OT E
If compressor fails one of the steps, then AC system should be diagnosed in order to find root cause of fail-
ure. Root cause of failure should be repaired.
Identifying compressors that function is purpose of this instruction. Compressors that function should be identified
before compressors are removed from machine. Compressors that function should produce both high pressure and low pres-
sure. If compressor fails any one of steps 3, 5, 7, or 8, compressor is considered to be a "failed" compressor.
Check air filters (TM 5-3805-291-10). If complaint of customer is poor cooling of cab, past experience has shown
plugged air filters can often be cause. Most AC systems have return air filters and fresh air filters. Be sure to check both
Test voltage. While engine is running and AC is switched ON, check voltage at compressor. Voltage at compressor
should be a minimum 23V. Routinely used electrical loads should be turned ON. For example, a lighting system which
is added by customer could cause available voltage to decrease below minimum specification.
Test resistance. Measure resistance of clutch coil at compressor connector. Measured resistance should be within -1.3 to
+5.5 of 17.6 + 0.6 Ohms. Resistance range which are listed above compensate for effect of temperature on clutch coil.
WAR N I N G
Accidental machine starting ca cause injury or death to personnel working on machine.
To avoid accidental machine staring, turn battery disconnect switch to OFF position and remove
key. If machine is not equipped with a battery disconnect switch, disconnect battery cables from
battery and tape battery clamps.
Place a do not operate tag at batery disconnect switch location to inform personnel that machine
is being worked on.
N OT E
Electrical power supply to compressor should be switched OFF in order to perform this test.
Test rotation. Rotate compressor in direction of belt travel by turning nut on end of main shaft of compressor. Rotation
should be smooth with no binding. If not, replace AC system compressor (WP 0221 00).
Check charge level (WP 0222 00). AC system must be correctly charged per specification or an incorrect diagnosis
will occur. Recovering, evacuating, and recharging with clean refrigerant to correct level is best method of achieving
correct refrigerant charge for system. Charging AC system must be conducted by weighing refrigerant with a calibrated
scale in order to ensure accuracy. Also, be sure to replace oil which was removed during refrigerant recovery with new
Test for low pressure (WP 0222 00). Test for low pressure should be performed with ambient temperatures of less than
86°F (30°C). Park machine in an area not in direct sunlight. Close all cab doors and windows. Block flow of fresh air
into cab. If AC system is equipped, bypass low pressure switch. Start machine. Operate machine at high idle. Turn ON
AC (TM 5-3805-291-10). Set cab blower on LOW. After 10 to 15 minutes of operation, measure low-side pressure at
refrigerant compressor. If pressure reading is less than 10 psi (69 kPa), then suction valves of compressor are operating
correctly. If not, replace AC system compressor (WP 0221 00).