MAINTENANCE OF M939 SERIES VEHICLES - OD1661 - LESSON 1/TASK 1
(14) Primary Air pressure Gage, indicates air pressure
(15) Defroster Control, opens vents to direct heated air at the
(16) Heat Vent Control, controls the amount of heat blown into the
cab by adjusting the opening of heat ventilation doors.
(17) Fresh Air Vent Control, pulls out to open ventilation doors,
allowing outside air to circulate in the cab.
(18) Spring Brake Release Control is pushed in to release the
spring brakes independently of the mechanical parking brake.
control is used to release the spring brakes in order to test and
adjust the mechanical brake.
Body Equipment Controls and Indicators - Medium Wrecker.
Key item numbers 1 through 12 and their function
coincide with figures 12 and 13 on pages 22 and
(1) Trailer Power Outlet Receptacle (figure 12) provides electric
power for the trailer.
Towing Pintle Hook, is opened to attach the trailer towing
(3) Emergency Air Coupling, is connected by an air coupling hose
to the emergency coupling of a trailer or vehicle to be towed. This
connection permits the towing vehicle to charge the brake system of a
trailer or disabled vehicle with air.
(4) Trailer Air Valve Handles, are turned to release compressed
air to the trailer brake system.
On the M931 and M932, the valve
handle is placed in the down (open) position.