System Diagnosis

NOTE: Perform the Blower Motor Test with the Ignition Switch in RUN, the Mode Selector in VENT, and the Blower Switch in HI.

1. BLOWER MOTOR TEST: Check the HTR A/C FUSE. Measure the voltages to ground at the BLOWER MOTOR with the connector in place.

Blower Motor Test.:

^ If the voltages at the motor are correct, connector pins are not loose, and the motor does not run, install a new BLOWER MOTOR.
^ If Battery voltage is present at the PPL wire, check the wire for opens, then test the Function Selector and the BLOWER RELAY.
^ If Battery voltage is at the BLK wire, check for an open ground.

NOTE: The A/C Mode Selector Test is to be performed with the Ignition Switch in RUN.

2. A/C MODE SELECTOR TEST: Backprobe the connector to the A/C CONNECTOR HEAD and measure the voltage to ground, with the connector still on the head.

A/C Control Head Test.:

^ If Battery voltage is not present at E, check the BRN wire circuit back to the fuse.
^ If Battery voltage is at E, but not at B, install a new A/C CONTROL HEAD.

NOTE: The Blower Switch Test is to be performed with the A/C Mode Selector in VENT, and the Ignition Switch in RUN.

3. BLOWER SWITCH TEST: Remove the connector from the BLOWER RESISTORS. Measure the voltage to ground on the connector to the A/C CONTROL HEAD, with the connector still on the head.

A/C Control Head Test.:

^ If any of the voltages above are not correct, install a new A/C CONTROL HEAD.

NOTE: The Blower Resistors Test is to be performed with the Ignition Switch in RUN, and the Blower Switch in LO.

4. BLOWER RESISTORS TEST: Backprobe the connector to the BLOWER RESISTORS with the connector still on the resistors, and measure the resistance between the wires listed below. The resistance values are approximate.

Blower Resistor Test.:

^ If resistors are open, or shorted, or different from the values given, install new blower resistors.

5. BLOWER RELAY TEST: Remove the connector from the BLOWER RELAY and measure the voltage to ground at each wire of the connector. Do this with the Ignition Switch in RUN, the Blower Switch in HI, and the Mode Selector in VENT.

Blower Relay Connector Test.:

^ If the voltage at a wire is not correct, check the circuit at that wire.

6. With the connector still removed from the BLOWER RELAY, measure the resistance to ground at the following connector terminals. First, disconnect the negative battery terminal.

Blower Relay Resistance Test.:

^ If the voltages and resistances at the BLOWER RELAY connector are correct, install a new relay.