Heating and Air Conditioning: Description and Operation

CIRCUIT OPERATION
Battery voltage from Fusible Link A is applied to the normally open contacts of the Blower Relay at all times. When the engine is running, battery voltage is applied to the coil of the A/C Blower Relay. With the other side of the Blower Relay coil grounded at G1OO (2.6L 4ZE1) or G107 with normal oil pressure (2.8L V6), the relay contacts close and battery voltage is applied to the A/C Blower In-line Fuse and Fuse 8.

Battery voltage from the A/C Blower In-line Fuse is applied to the Blower Switch and the Blower Resistors through the normally open contacts of the Blower Cut-out Relay.

With the Blower Switch in LOW, all of the Blower Resistors are in the circuit and the Blower Motor, which is grounded at G1O1, runs at its slowest speed. With the Blower Switch in the MEDIUM 1 (M1) or MEDIUM 2 (M2) position, some of the Blower Resistors are bypassed and the Blower Motor will run at a faster speed.When the Blower Switch is in the HIGH (H) position and the Mode Control Switch is in any position except HEAT, the Blower Motor receives battery voltage through one resistor.

Battery voltage from Fuse 8 is applied to the Blower Switch and to the Mode Control Switch. When the Blower Switch or the Mode Control Switch is turned to the OFF position, battery voltage is applied to the coil of the Blower Cut-out Relay. The other side of the coil is connected to ground G1O1. Applying voltage to the coil of the Blower Cut-out Relay causes the relay contacts to close and remove voltage from the Blower Switch and the Blower Resistors. The Blower Motor stops.

HEATER HIGH SPEED OPERATION
When the Blower Switch is in HIGH (H), battery voltage is applied to the Blower Resistors and to the Heater High Speed Blower Relay. With the Mode Control Switch in HEAT, battery voltage is applied to one side of the relay's coil. The other side of the coil is grounded at G1O1. This causes the relay contacts to open, removing battery voltage directly from the Blower Motor.