2-3. CHASSIS CONTROLS AND INDICATORS (Contd)
Item and Function
PRIMARY AIR PRESSURE GAUGE indicates air pressure in the primary brake system. Normal pressure is 90-
130 psi (621-896 kPa).
DEFROSTER CONTROL opens vents to direct heated air at the windshield.
HEAT VENT CONTROL controls the amount of heat blown into the cab by adjusting the opening of heat
FRESH AIR VENT CONTROL pulls out to open ventilation doors, allowing outside air to circulate in the cab.
GRAB HANDLE aids crewmembers in entering and exiting vehicle cab. Handle is also a brace for crewmembers
FLOODLIGHT CONTROL SWITCH (M936/AI/A2 models) turns on floodlights installed on wrecker body for use in
night crane operations.
ELECTRICAL RECEPTACLE OUTLET (M936/A1/A2 models) provides battery voltage for extension cord trouble
AUXILIARY OUTLET RECEPTACLE (M936/A1/A2 models) is plugged into electrical receptacle outlet. A trouble
light is then plugged into the auxiliary outlet receptacle in order to be powered by vehicle batteries.
SPRING BRAKE RELEASE CONTROL is pushed in to release spring brakes independently of the mechanical
parking brake. Control is used to release spring brakes in order to test and adjust mechanical brakes.
VOLTMETER indicates charging condition of the batteries.
SECONDARY AIR PRESSURE GAUGE indicates air pressure in the secondary brake system. Normal pressure
is 90-130 psi (621-896 kPa).
TRANSMISSION OIL TEMPERATURE GAUGE indicates temperature of transmission oil. Normal operating
temperature is 120°-220°F (49°-104°C).
ENGINE OIL PRESSURE GAUGE indicates oil pressure when engine is running. Normal operating pressure at
idle is 15 psi (103 kPa).
FUEL GAUGE indicates fuel level in fuel tank(s).
AMBER WARNING LIGHT SWITCH (M936/A1/A2 models) controls operation of amber warning light used during
crane operations or while towing disabled vehicle.
TRAILER AIR SUPPLY VALVE (M931/A1/A2 and M932/A1/A2 models) is pushed in to supply air to the brake
system of towed trailer or semitrailer.
EMERGENCY ENGINE STOP CONTROL is pulled out to cut off fuel to engine. It is used only in an emergency.
HEATER BLOWER MOTOR SWITCH activates heater blower.
WIPER MOTOR SWITCHES activate and controls speed of wiper.
WINDSHIELD WASHER CONTROL sprays cleaning solution on windshield when depressed.