COMPRESSOR 0821072 - Caterpillar

An open circuit breaker will close (reset) automatically when it becomes cooler.Electronic Speed Switch
Electronic Speed Switch
(1) Reset button. (2) Lamp.The electronic speed switch (dual speed switch) activates the shutoff solenoid when the engine speed gets approximately 18 percent higher than the rated full load speed of the engine. It also stops current flow to the starting motor after the engine starts.The electronic speed switch makes a comparison between the output frequency of the magnetic pickup and the setting of the electronic speed switch. When they are equal, the normally open contacts in the electronic speed switch close. Lamp (2) will go on. The switch also has a failsafe circuit that will cause the engine to shutdown if there is an open in the magnetic pickup circuit.When the engine is stopped, it will be necessary to push reset button (1), before the engine can be started.Starting System Components
Solenoid
Typical Solenoid SchematicA solenoid is a magnetic switch that does two basic operations.a. Closes the high current starting motor circuit with a low current start switch circuit.b. Engages the starting motor pinion with the ring gear.The solenoid switch is made of an electromagnet (one to two sets of windings) around a hollow cylinder. There is a plunger (core) with a spring load inside the cylinder that can move forward and backward. When the start switch is closed and electricity is sent through the windings, a magnetic field is made that pulls the plunger forward in the cylinder. This moves the shift lever (connected to the rear of the plunger) to engage the pinion drive gear with the ring gear. The front end of the plunger then makes contact across the battery and motor terminals of the solenoid, and the starting motor begins to turn the flywheel of the engine.When the start switch is opened, current no longer flows through the windings. The spring now pushes the plunger back to the original position, and at the same time, moves the pinion gear away from the flywheel.When two sets of windings in the solenoid are used, they are called the hold-in winding and the pull-in winding. Both have the same number of turns around the cylinder, but the pull-in winding uses a larger diameter wire to produce a greater magnetic field. When the start switch is closed, part of the current flows from the battery through the hold-in winding, and the rest flows through the pull-in windings to the motor terminal, then through the motor to ground. When the solenoid is fully activated (connection across battery and motor terminal is complete), current is shut off through the pull-in windings. Now only the smaller hold-in windings are in operation for the extended period of time it takes to start the engine. The solenoid will now take less current from the battery, and heat made by the solenoid will be kept at an acceptable level.Electric Starting System
The starting motor is used to turn the engine flywheel fast enough to get the engine to start running.The starting