Functional Check of Heater Blower Motor Drive and Electrical Circuit Components; Component Replacement

PROCEDURE

1. Check the condition of all terminal connections in the corresponding electrical circuit. Make sure the battery is fully charged. Check fuse No. 56 in the engine compartment fuse/relay box, and fuse No. 3 in the junction block located under the left side of the instrument panel.
2. Locate the heater blower motor relay in the engine compartment fuse/relay box. Remove the relay and check its operation (see Chapter Electrical). Replace a faulty relay.
3. Place the transmission in "P", apply the parking brake, and turn the ignition key to ON without starting the engine.

4. The heater blower assembly is located under the instrument panel, behind the glove box, near the engine compartment bulkhead.

5. Set the air direction control on the heater control panel to FLOOR and the blower speed selector to 4. Listen to determine whether air is flowing through the ducts. If air flows, set the speed selector to 1 and listen again. Repeat the check at each speed position.

The blower speed switch is connected to the blower motor circuit on the ground side.

6. If the fan does not operate and all fuses and relays have been checked and are serviceable, check the blower motor itself. Locate the electrical connector on the rear of the blower assembly. With the ignition on, probe the yellow/black wire terminal with a sharp-tipped voltmeter probe. Battery voltage of at least 10 V must be present at this terminal in any blower speed position except OFF. If not, there is a fault in the circuit between the fuse junction block and the heater/A/C control panel, or between the control panel and the blower motor.

7. If voltage is present at the supply terminal but the fan does not operate, ground the blue/red wire terminal to chassis ground (use a jumper wire with a sharp probe). If the fan does not operate when the terminal is grounded, replace the blower motor. Otherwise, check the circuit between the blower speed selector switch and the resistor assembly.

8. If the fan operates only at some speeds, check the blower resistor. The resistor assembly is mounted on the right side of the fan housing under the instrument panel. The board contains three resistors that provide the three lower blower speeds. At maximum speed (position 4), current bypasses the resistors.
9. Remove the resistor assembly and visually inspect its elements (elements must not be burnt or melted). Measure the resistance between terminals 1 and 5 of the connector. If the reading is outside the range 5 ÷ 3.5 Ohm, replace the assembly.

10. If the resistor assembly is serviceable but the fan still does not operate at all speeds, refer to the Body Electrical section and remove the heater/A/C control panel. Disconnect the wiring connector from the rear of the fan speed selector switch and check continuity between the contact terminals in the different switch positions. Replace a faulty switch.

11. Check the heater fan relay in the junction block in the engine compartment. Remove the relay from its socket and check its operation (see Body Electrical chapter). Probe the contact terminals in the junction block socket with a voltmeter: terminal 4 must have battery voltage at all times, terminal 1 only with the ignition on. Terminal 2 must be permanently grounded to chassis.