HOUSING 8J0475 - 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. The “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.A/C Thermostat Switch
Illustration 5 g03089222The thermostat switch acts as a limit switch. The switch alerts the ECM when the temperature of the evaporator coil has exceeded a specific value. The ECM uses this data to manage the HVAC system for the machine.A/C Manual Mode Switch
Illustration 6 g03089540The air conditioning manual/auto mode switch has a normally open contact and a normally closed contact. The contacts provide switch to ground inputs to the ECM to indicate the position of the switch. When in manual mode the A/C is activated. When in auto mode, the ECM determines if the A/C should be activated.High-Pressure Switch
Illustration 7 g03099857The high-pressure switch acts as a limit switch. The switch alerts the ECM when the pressure exceeds a certain point on the outlet of the A/C compressor. The switch prevents operation of the A/C compressor during conditions of overcharge of the refrigerant.Low-Pressure Switch
Illustration 8 g03099916The low-pressure switch acts as a limit switch. The switch alerts the ECM when the pressure drops below a certain point on the inlet of the A/C compressor. The switch prevents operation of the A/C compressor during conditions of undercharge.Outputs
Relays
A/C Clutch Relay
Illustration 9 g03126958The A/C clutch relay controls the operation of the clutch on the compressor.A/C Clutch
Illustration 10 g03032419
Illustration 11 g03099957
(1) Magnetic clutch and pulley assembly
(2) Coil assembly
(3) Drive plate
(4) Bearing
(5) Compressor shaftThe machine ECM energizes the air conditioning clutch when the operator requests and system status generate a request for air conditioning.The compressor is driven by the engine. A belt connects the engine to the clutch and pulley assembly (1). The pulley assembly is located on the clutch. The drive plate (3) is fastened to the shaft of the compressor. The clutch and pulley assembly (1) turns on the bearing (4). The clutch and pulley assembly (1) are not connected to the shaft (5). The electric current from the thermostat controls a magnetic field in the coil assembly (2).The magnetic field pulls the drive plate (3) against the clutch and pulley assembly (1). The clutch and the pulley assembly (1) turn shaft (5) that operators the compressor. When the current to the coil assembly (2) is stopped, the magnetic field is removed. The field removal allows the drive plate (3) to move away from the clutch and pulley assembly (1). The clutch and pulley assembly (1) will turn freely on the bearing (4). The sequence of connecting and disconnecting the pulley to the compressor shaft (5) is called compressor cycling. The compressor cycling is controlled by the thermostat. The thermostat is controlled by the capillary tube, which is installed between the fins of the evaporator coil.A/C Condensers Relays
Illustration 12 g03090316The two A/C condenser relays