A/C System - Manual

OPERATION
Blower Circuits
With the Ignition Switch in RUN, voltage is present at the Heater Control Assembly Blower Switch through the HEATER Circuit Breaker, the Blower Motor winding and the Blower Motor Resistor.

With the Blower Switch in any position but OFF, current flows through the HEATER Circuit Breaker, the Blower Motor winding, the Blower Motor Resistors and the Blower Switch to ground.

The Blower Motor runs at speed "1," "2," "3," or "4," depending on Blower Motor Switch position.
^ In position "1" current must pass through three dropping resistors, so the blower motor runs at a slow speed.

^ In position "2" current passes through two dropping resistors, and the blower motor runs faster.

^ In position "3" current passes through one dropping resistor, so the blower motor runs still faster.

^ In position "4" current bypasses all dropping resistors, so the blower motor runs at the fastest speed.

Vehicles equipped with the Blower Switch in any position but OFF, a "blower on" input is provided to pin S of the EGI Control Module.

Compressor Circuits
Voltage is present at the [1][2]A/C Relay contacts at all times through the A/C fuse.

With the Ignition Switch in RUN, voltage is present at the [1][2]A/C Relay coil through the REAR WIPER Fuse. Voltage is also present at the A/C-Heater Control Assembly A/C Switch through this fuse and the A/C ON Indicator bulb.

Pressing the A/C Switch causes its contacts to close, grounding pin Q of the EGI Control Module. Also, current flows through the REAR WIPER Fuse, the A/C ON Indicator, the A/C Switch and the Blower Switch to ground. The A/C On Indicator illuminates.

With pin Q grounded, the EGI Control Module has an "A/C demand" input, and the Module grounds pin J (unless a special condition, like wide open throttle, exists). With pin J grounded, the [1][2]A/C Relay coil is grounded, the coil energizes and the Relay contacts close. Current flows through the A/C Fuse, the A/C Relay contacts, the Clutch Cycling Pressure Switch contacts and the A/C Clutch Field Coil to ground. The A/C Clutch Field Coil energizes, the A/C clutch engages and the A/C compressor runs.

The compressor runs until system low side pressure drops to about 24.4 psi, at which time the Clutch Cycling Pressure Switch contacts open, deenergizing the A/C Clutch Field Coil.

The Clutch Cycling Pressure Switch opens and closes as low side pressure drops and rises to maintain the proper temperature at the evaporator core.

With pin J of the EGI Control Module grounded, circuit 713 (BK/DG) to the Cooling Fan Relay is also grounded, causing the Electric Cooling Fan to run.