HOOD AS 3893578 - Caterpillar

Electrical Side Of The Air System
Move the start control switch in order to activate the starting solenoids. Listen for the sound of the engagement of the air starter motor pinion with the flywheel gear.
If the sound of the engagement can be heard, the problem is with the Air Side Of The Air System. Proceed to the Air Side Of The Air System.
If no sound of the engagement can be heard, the problem could be with the Electrical Side Of The Air System.
Illustration 1 g00286936
Control valve (typical example)
(1) Control valve
(2) Connector
Check the electrical system by disconnecting the leads from the control valve (1) at connector (2). Set the multimeter in the "DCV" range. Measure voltage across the disconnected leads that connect to the starting switch.
A voltage reading shows that the problem is in the control valve (2) or the air starting motor. Go to Step 2 of Air Side Of The Air System.
A "ZERO" reading shows that the problem is in the control switch or the problem is in the wires for the control switch.
Fasten the multimeter lead to the start switch at the terminal for the wire from the battery. Fasten the other lead to a good ground.
A "ZERO" reading indicates a broken circuit from the battery. With this condition, check the circuit breaker and wiring.
The problem is in the control switch if either a voltage reading is found at the control switch or if a voltage reading is found in the wires from the control switch to the control valve. Air Side Of The Air System
Illustration 2 g00286937
Air starting system (typical example)
(1) Control valve
(2) Connector
(3) Connection
(4) Air hose
(5) Relay valve
Activate the control switch. If the engagement of the air starter motor pinion with the flywheel ring gear can be heard then remove the small air hose (4) from the top of the relay valve (5).
Full air pressure comes from the end of the air hose (4) when the control switch is activated. The relay valve (5) is worn or the air starting motor is damaged.
If no air pressure comes from the end of the air hose (4), then the problem is in the pinion nose housing for the air starting motor.
The sound of the air starter motor pinion is not heard when the control switch is activated. Voltage was measured at the control valve. Remove the other small air hose from the connection (3).
If no air comes from the end of the removed air hose, the control valve (1) is worn.
If the air comes from the end of the removed hose, then the problem is in the pinion nose housing for the air starting motor.