| • | Perform the Diagnostic System Check . Refer to Diagnostic System Check - Vehicle . |
| • | Review Strategy Based Diagnosis. Refer to Strategy Based Diagnosis . |
| • | Diagnostic Procedure Instructions provide an overview of each diagnostic category. |
Circuit/System Description
The auxiliary blower motor is a variable speed fan. The Auxiliary HVAC enabling switch provides negative ground to the auxiliary HVAC circuit refer to HVAC Schematics . The Auxiliary Heater and Air Conditioning Control varies the voltage drop across the auxiliary blower motor in relation to the pulse width modulated signal. The auxiliary blower motor speed can be adjusted from 10 percent to 90 percent duty cycle (PWM), 90 percent is considered high speed fan. During normal operation the control circuit voltage will be low and near battery voltage when OFF.
Reference Information
Schematic Reference
HVAC Schematics. Refer to HVAC Schematics .
Connector End View Reference
HVAC Connector End Views. Refer to HVAC Connector End Views .
Description Operation
Air Delivery Description Operation. Refer to Air Delivery Description and Operation .
Electrical Information Reference
| • | Circuit Testing. Refer to Circuit Testing . |
| • | Connector Repairs. Refer to Connector Repairs . |
| • | Testing for Intermittent Conditions and Poor Connections. Refer to Testing for Intermittent Conditions and Poor Connections . |
| • | Wiring Repairs. Refer to Wiring Repairs . |
Circuit/System Verification
Ignition ON, ensure the auxiliary HVAC Enabling Switch is activated. Command the auxiliary blower motor ON and OFF at the Auxiliary Heater and Air Conditioner Control Module. Observe that the auxiliary blower motor turns ON and OFF with each command.
Circuit/System Testing
Ignition ON, ensure the auxiliary HVAC Enabling Switch is activated. Command the auxiliary blower motor ON and OFF at the Auxiliary Heater and Air Conditioner Control Module. Observe that the and the auxiliary blower motor turns ON and OFF with each command.
- Ignition OFF, disconnect the harness connector at the Auxiliary Blower Motor Control Module.
- Ignition OFF, test for less than 1.0 ohm of resistance between the ground circuit terminal 5 and ground.
- Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 6 and ground.
- Test for the following voltages between the control circuit terminal 3 and ground with the auxiliary blower motor speed set at the specified levels:
- If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the Auxiliary Heater and Air Conditioner Control Module.
- If less than the specified range, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC Control Module.
If greater than 1.0 ohm, test the ground circuit for an open/high resistance
If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the REAR HVAC fuse is open, test battery positive voltage circuit for a short to ground.
Off--Less than 1 volt
Level 1--7.5-8.5 volts
Level 2--8.5-9.5 volts
Level 3--9.5-10.5 volts
