Voltage is supplied to the auxiliary heater blower motor switch from the auxiliary blower motor relay. The auxiliary HVAC control assembly applies voltage to the auxiliary blower motor control circuit that corresponds to the selected blower speed. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the auxiliary blower motor per particular speed request:

When the operator requests High speed, voltage is applied directly to the auxiliary heater blower motor.

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Manual HVAC Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, place the auxiliary blower switch in the LO, MED and HI speed positions. The blower motor should operate in each speed position.

1. Ignition OFF, disconnect the auxiliary blower motor relay.
2. Test for less than 1.0 ohm between the ground circuit terminal 85 and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

3. Verify that a test lamp illuminates between the ignition circuit terminal 86 and ground.

⇒	If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse/circuit breaker is open, test or replace the auxiliary blower motor relay.

4. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit breaker is open, test the output circuit terminal 87 for a short to ground.

5. Ignition OFF, connect the auxiliary blower motor relay. Disconnect the harness connector at the auxiliary HVAC control assembly.
6. Ignition ON, verify that a test lamp illuminates between the control circuit terminal G and ground.

⇒	If the test lamp does not illuminate, test the output circuit for an open/high resistance. If the circuit tests normal, test or replace the auxiliary blower motor relay.

7. Ignition OFF, connect the harness connector auxiliary HVAC control assembly. Disconnect the harness connector at the auxiliary blower motor resistor.
8. Ignition ON, while cycling the auxiliary blow motor switch between LO, MED, and HI, verify that a test lamp illuminates between the appropriate blower motor control circuit terminal listed below and ground:

•	LO - terminal C

•	MED - terminal A

•	HI - terminal B

⇒	If the test lamp does not illuminate, test the appropriate control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the auxiliary HVAC control assembly.

9. Ignition OFF, connect the harness connector at the auxiliary blower motor resistor. Disconnect the harness connector at the auxiliary blower motor.
10. Test for less than 1.0 ohm between the ground circuit terminal B and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

11. Connect a test lamp between the control circuit terminal A and the ground circuit terminal B.
12. Ignition ON, cycle the blower motor switch between LO, MED and HI speeds. The test lamp should illuminate and change in intensity as the blower speed is varied.

⇒	If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the blower motor resistor assembly.

⇒	If the test lamp does not change intensity, test the control circuit for a short to voltage. If the circuit tests normal, test or replace the blower motor resistor assembly.

13. If all circuits test normal, test or replace the auxiliary blower motor.

Auxiliary Blower Motor Relay

1. Ignition OFF, disconnect the auxiliary blower motor relay.
2. Test for 60-180 ohms between terminals 85 and 86.

⇒	If the resistance is not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

•

30 and 86

•

30 and 87

•

30 and 85

•

85 and 87

⇒	If not the specified value, replace the relay.

4. Install a 30-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87.

⇒	If greater than the specified range, replace the relay.

Blower Motor

1. Ignition OFF, disconnect the harness connector at the auxiliary blower motor.
2. Install a 30-amp fused jumper wire between the control circuit terminal A and 12 volts. Install a jumper wire between the ground circuit terminal A and ground. Verify the auxiliary blower motor activates.

⇒	If the blower motor does not activate, replace the auxiliary blower motor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.