Compressor HVAC: Description and Operation

V-5 Compressor Mounted Control Switches (VIN U):

COMPRESSOR CONTROLS

CIRCUIT OPERATION
The compressor for the A/C System is belt-driven by the engine through the A/C Compressor Clutch. The clutch allows the compressor to be disengaged when A/C is not required, or to remove the A/C load from the engine when needed.

Operation of the compressor depends on the mode selected by the driver, When the Mode Selector Switch is in MAX, NORM, BI/L or DEF, battery voltage is applied through the HTR-A/C Fuse, the Heater and A/C Control Assembly and the A/C Pressure Cut-Out Switches to the A/C Compressor Control Relay.

For vehicles equipped with the L4 VIN U engine, the path to the A/C Compressor Control Relay is through the A/C Low Pressure Cut-Out Switch and the A/C High Pressure Cut-Out Switch, which are both normally closed. The A/C Low Pressure Cut-Out Switch opens if the refrigerant charge is too low for operation of the compressor without possible damage to it. The A/C High Pressure Cut-Out Switch opens if the refrigerant pressure becomes too high for normal operation.

The A/C Compressor Control Relay is operated by the Engine Control Module (ECM). When the ECM receives the A/C ON signal (Battery voltage at terminal 2 of connector C2),the ECM grounds the A/C Compressor Control Relay at terminal 3, of connector C1 energizing the relay. When the A/C Compressor Control Relay is energized, voltage is applied to the A/C Compressor Clutch.

If the ECM determines that the engine load should be reduced, such as during full throttle, the ECM de-energizes the A/C Compressor Control Relay. This removes voltage from the A/C Compressor Clutch, removing the A/C load from the engine. A similar action takes place under high steering loads, which causes the Idle Speed Power Steering Pressure Switch to close. When the Idle Speed Power Steering Pressure Switch closes, it signals the ECM to de-energize the A/C Compressor Control Relay.