Circuit Operation

CIRCUIT OPERATION

BLOWER CONTROLS

In all blower speeds except HI, the HTR-A/C Fuse supplies current to the Blower Motor. In high speed operation, current from the Blower Switch energizes the High Blower Relay, permitting current to flow from the Battery Junction Block to the Blower Motor.


BLOWER LOW SPEED OPERATION

The Blower Motor only operates in Low Speed through the A/C-Heater Selector Switch. With the A/C-Heater Selector Switch in MAX A/C, NORM A/C, BI-LEVEL, VENT, HEAT, or DEFROST, power through the A/C-Heater Selector Switch is available to the Blower Resistors through the BRN/WHT (64) wire. The current then flows through all three resistors and the normally closed contacts of the High Blower Relay to the Blower Motor and the Blower Motor runs at Low speed.


BLOWER MEDIUM LOW SPEED

OPERATION

With the Blower Switch in M1, current flows from the HTR-A/C-Fuse, through the A/C-Heater Selector Switch, the BRN/WHT (64) wire and the Blower Switch to the TAN (63) wire at the Blower Resistors. Current then flows through two of the resistors and the normally closed contacts of the High Blower Relay to the Blower Motor. The Blower Motor then runs at Medium Low speed.


BLOWER MEDIUM HIGH SPEED

OPERATION

With the Blower Switch in M2, the blower operates the same as in the Medium Low speed, except that the current is directed to the Blower Resistors through the LT BLU (72) wire. Current passes through only one resistor. The Blower Motor then runs at Medium High speed.


BLOWER HIGH SPEED OPERATION

With the Blower Switch in HI, current bypasses the Blower Resistors and flows to the High Blower Relay through the ORN (52) wire. This current energizes the relay and closes the normally open contacts of the relay. Current then flows from the Battery Junction Block, through the relay to the Blower Motor, and the Blower Motor runs at High speed.


COMPRESSOR CONTROLS

The Compressor for the Air Conditioning System is driven by the engine by means of a belt drive and the A/C Compressor Clutch. The Clutch allows the Compressor to be disengaged when Air Conditioning is not required. Power to the A/C Compressor Clutch is supplied by the HTR-A/C Fuse.


The A/C Compressor Clutch Diode is connected across the terminals of the A/C Compressor Clutch. Whenever the clutch is de-energized, the magnetic field around it collapses, generating an induced voltage in the clutch coil. The Diode provides a path for the current resulting from the induced voltage so other circuit components are not damaged.


With the A/C-Heater Selector Switch in any mode except VENT or HEAT, current flows from the Selector Switch LT GRN (66) wire through the Low Pressure Switch and the DK GRN/WHT (459) wire to the A/C Control Relay terminal B and the Electronic Control Module (ECM).

The A/C Request signal to the ECM closes the A/C Cutout Switch in the ECM providing a ground through the DK BLU (458) wire at terminal C of the A/C Control Relay. This allows current to flow from the IGN/ GAUGES Fuse to terminal A of the A/C Control Relay, energizing the relay. Current from the HTR-A/C Fuse then flows through the closed contacts of the relay to energize the A/C Compressor Clutch. The A/C Request signal to the ECM also increases engine idle speed.


The A/C Compressor can be turned off in one of three ways:

1. Moving the Function Lever to the VENT or HEAT position on the A/C-Heater Selector Switch stops the current flow to the system from the HTR-A/C fuse.

2. If the A/C system pressure drops too low, the Low Pressure Switch will open stopping the current flow.

3. If, while turning the vehicle, power steering system pressure rises above 3792 kPa (550 psi), the Power Steering Pressure Switch opens. This interrupts the ground signal to the ECM causing the A/C Cutout switch in the ECM to open, deenergizing the A/C Control Relay. When the power steering system pressure drops below 3792 kPa (550 psi), the Power Steering Pressure Switch closes and the A/C Compressor again starts operating.