TM-9-2320-272-23-1
TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL)
TECHNICAL MANUAL; FIELD MAINTENANCE MANUAL; VOLUME 1 OF 5
SEPTEMBER 2012
TM-9-2320-272-23-1 - Page 251 of 1313
AUXILIARY AIR-POWERED SYSTEM OPERATION
The auxiliary air-powered system consists of air-actuated vehicle accessories. All of these accessories receive air
pressure through the accessory manifold and off the pressure protection valve with the exception of the horns.
Components of the auxiliary air-powered system are:
A. WINDSHIELD WIPER CONTROL SWITCH
- Opens air pressure valve in wiper motor to operate wipers.
B. WINDWHIELD WIPER MOTOR
- Air-actuated motor powers windshield wipers.
C. WINDSHIELD WASHER CONTROL
- Spring-loaded valve that allows air pressure to force washer fluid
from washer reservoir to windshield.
D. WINDSHIELD WASHER RESERVOIR
- Container for windshield washer fluid.
E. ACCESSORY MANIFOLD
- Receives air pressure from the pressure protection valve and distributes it
to the various accessories.
F. FRONT-WHEEL DRIVE LOCK-IN SWITCH
- Air-actuated switch that engages front-wheel drive when
transfer case is in HIGH.
G. WINDSHIELD WASHER NOZZLES
- Direct washer fluid on windshield.
H. GOVERNOR
- Serves as a tee between accessory manifold and horn relay valve. It also signals the air
compressor to stop compressing air for the supply system when operating pressure has been reached.
I. TRANSFER CASE AIR SHIFT CYLINDER
- Engages front-wheel drive when it receives air pressure from
lock-in switch or engagement control valve.
J. FRONT AXLE ENGAGEMENT CONTROL VALVE
- Operates off cam, on transfer case shift linkage so
front-wheel drive engages automatically when transfer case is put into LOW.
K. HORN RELAY VALVE
- Electrical signal from horn button on steering wheel opens valve in horn relay,
allowing air pressure to sound horns.
L. HORNS
- Receive air pressure from horn relay valve to sound off.
TM 9-2320-272-23-1
0003
0003-46
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