MOUNT 3019825 - Caterpillar

The 155-4652 Solenoid (Fuel Shutoff) (24 volt) and the 155-4651 Solenoid (Fuel Shutoff) (12 volt) are often wrongly replaced. The following sections explain solenoid operation and provide troubleshooting guidance.Construction
Illustration 1 g00736320
Solenoid Assembly (1) Start terminal - positive (No. 8-32 THD) (2) Stop terminal - positive (No. 8-32 THD) (3) GND terminal - negative (No. 10-32 THD) (4) Plunger release button (5) Plunger - in the ON position (6) Plunger - in the OFF position (7) Plunger spring
Illustration 2 g00736552
Schematic symbol (8) Ground Terminal (9) Stop coil (10) Stop terminal (11) Start terminal (12) Start Coil (13) Internal switchThe major parts of a solenoid are listed below:Start Coil - The start coil (12) is energized when the key switch is in the START position.Stop Coil - The Stop Coil (9) is energized when the key switch is in the OFF position.Internal Switch - The internal switch (13) controls the operation of the start coil and the stop coil.Plunger - The plunger (5,6) is retracted for engine run mode. The plunger is extended for engine stop.Plunger Spring - The plunger spring (7) pushes the plunger out to the STOP position.Permanent Magnet - The permanent magnet holds the plunger in for the run mode.Plunger Release Button - If electrical system power is not available, the plunger release button (4) allows for manual engine shutdown.Operation
When the key switch is turned to the start position, the start coil is energized. Current flows through the start coil through the internal switch. Current exits the start coil through the ground terminal. A magnetic field is created by the start coil. This magnetic field retracts the plunger.
When the plunger is retracted (engine run position), the internal switch opens the start coil circuit. When the permanent magnet holds the plunger in the engine run position, no current flows through the solenoid.
When the key switch is turned to the OFF position, the stop coil is energized. After the stop coil is energized, current will flow in the following pattern: through the stop coil, through the internal switch and out the ground terminal. The magnetic field created by the stop coil cancels the magnetic field of the permanent magnet. In order to stop the engine, the plunger spring pushes the plunger out. When the plunger is extended (stop position), the internal switch opens the stop coil circuit.Troubleshooting
If a problem is suspected with the operation of the solenoid, perform the following checks before replacing the solenoid. In order to perform this procedure, choose one of the multimeters from Table 1.
Table 1
TOOLS NEEDED    
Tool     Part Number    
Caterpillar Digital Multimeter     9U-7330    
Caterpillar Digital Multimeter     6V-7070    
Caterpillar Digital Multimeter     146-4080    
With