Driver Controls and Instruments trailer air supply system and release the trailer spring parking brakes. Before disconnecting a trailer or when operating a vehicle without a trailer, pull the trailer air supply valve knob out. 1 Air Suspension Dump Valve, Optional 3 The air suspension dump valve allows the air in the ve- hicle air suspension to be quickly exhausted, lowering the rear of the vehicle. This makes it easier to connect to or disconnect from a trailer. A dump valve toggle switch on the dashboard exhausts and fills the air sus- pension. To prevent accidental activation, a safety re- lease button on the switch must be pushed before the switch can toggle. See Fig. 3.16 .
2 CAUTION 10/28/94 f600543a 1. Parking Brake Control Valve Knob 2. Trailer Air Supply Valve Knob 3. Dump Valve Toggle Switch Never exhaust air from the suspension while driv- ing. If the air is exhausted, the suspension will not absorb road shocks and could be damaged. Fig. 3.16, Brake Valves/Air Suspension Dump Valve (typical switch locations) AirLiner Plus Suspension, Optional The AirLiner Plus suspension is used on vehicles with pusher or tag axles to improve traction performance. The system maintains an accurate leveling of frame height whether the vehicle is in motion or parked.
The Meritor WABCO ® ECAS (Electronically Controlled Air The red octagonal knob operates the trailer air supply valve. See Fig. 3.16 . After the vehicle and its air hoses are connected to a trailer and the pressure in the air system is at least 65 psi (447 kPa), push the trailer air supply valve knob in (it should stay in) to charge the 3.14