DOWEL 3066038 - Caterpillar

Switches
Switches provide an open signal, a ground signal, or a +battery signal to the inputs of the ECM. Switches are open or closed.
When a switch is open, no signal is provided to the corresponding input of the ECM. This “no signal” condition is also called “floating”.
When a switch is closed, a ground signal or a +battery signal is provided to the corresponding input of the ECM.Air Conditioning Mode Switch
Illustration 7 g03325737The air conditioning mode switch is a two pole switch. The switch has two positions that control the operation of the air conditioning. In the automatic position the ECM controls the operation of the air conditioning to maintain a specified cab temperature. In the manual position, the air conditioning is manually engaged. The ECM has two contacts that pertain to this switch, one signals the ECM the switch is automatic mode, the other signals the ECM the switch is in manual mode. These contacts will float to a high-voltage state unless the switch is closed to that contact. When the switch closes to a contact, the contact is pulled to a low or ground voltage state.Air Conditioning Low-Pressure Switches
Illustration 8 g03441357
(1) High-pressure side low-pressure switch
(2) Low-pressure side low-pressure switch
(A) To ECM Air Conditioning Refrigerant contact
(B) To power source entering A/C relayThe air conditioning low-pressure contact at the ECM monitors the voltage state of the high and low-pressure cutoff switches for the air conditioning. The switches are set up in series from a power source. The switches close and allow power to pass when the pressure in the high pressure and low pressures air conditioning loops is high exceeds the actuation pressure for the switch. If both switches have been actuated, both switches are closed and power flows from the power source to the ECM contact alerting the ECM that the air conditioning circuit isOutputs
The ECM responds to decisions by sending electrical signals to the outputs. The outputs can create an action or the outputs can provide information to the operator or the service technician.Relays
Air Conditioning Compressor Clutch Relay
Illustration 9 g03323937The air conditioning compressor clutch relay is an electric switch that is controlled by the ECM. The relay controls power to the air conditioning clutch solenoid. When the ECM sends a signal to the relay, the relay activates allowing power to flow to the solenoid, activating the solenoid, and causing the clutch to allow the air conditioning compressor to start.Condenser Fan Relay
Illustration 10 g03352416The condenser fan relays control the operation of the condenser fans. The relay is activated by the ECM when the air conditioning system is active. When the relay is activated, the relay allows power to flow to the condenser fans. When the ECM has not activated the relay, power is not allowed to flow to the condenser fans.Actuators
Water valve Actuator
Illustration 11 g03091818The water valve actuator controls the amount of heat that enters the HVAC system. When the water valve actuator is activated, the water valve opens and allows heat from the engine into the heater coils. The water valve is controlled