Auxiliary Blower Motor Malfunction (RPO C69 W/O Rear Controls)
Auxiliary Blower Motor Malfunction (RPO C69 W/O Rear Controls)
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
The front auxiliary HVAC control assembly applies a ground to the appropriate auxiliary blower motor relay 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 blower motor per particular speed request:
* Low speed, 2 resistors
* Medium speed, 1 resistor
When high fan speed has been selected, the blower motor switch applies a ground to the coil side of auxiliary high speed blower motor relay which energizes the relay and provides B+ voltage to the auxiliary blower motor.
Reference Information
Schematic Reference
HVAC Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector End Views By Name)
Description and Operation
* Air Temperature Description and Operation (Air Temperature)
* Air Delivery Description and Operation (Air Delivery)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Verification
Ignition ON, cycle the front auxiliary HVAC control assembly blower switch between the LOW, MED and HIGH speed positions. The blower motor should operate at the appropriate speed in each position.
If the blower motor is inoperative at all speeds, refer to Blower Motor Inoperative.
If the blower motor is inoperative in only one speed or does not change speed when cycling between the speed positions, refer to Blower Motor Malfunction.
Circuit/System Testing
Blower Motor Inoperative
1. Ignition OFF, disconnect the harness connector at the front auxiliary HVAC control assembly.
2. Ignition OFF, test for less than 5 ohms between the ground circuit terminal F and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
3. Ignition OFF, connect the harness connector at the front auxiliary HVAC control assembly. Disconnect the auxiliary high speed blower motor relay.
4. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal C2 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 is open, test the relay coil ignition circuit at each of the auxiliary blower motor relays for a short to ground. If the circuits test normal, replace the appropriate relay.
5. Verify that a test lamp illuminates between the B+ circuit terminal C1 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 fuse is open, test the relay switch B+ circuit at each of the auxiliary blower motor relays as well as the relay switch output control circuits for a short to ground.
6. Ignition OFF, disconnect the harness connector at the auxiliary blower motor.
7. Test for less than 5 ohms between the ground circuit terminal A and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
8. Connect the harness connector at the auxiliary blower motor.
9. Ignition ON, connect a 30A fused jumper wire between the B+ circuit terminal C1 and the control circuit terminal A2. Verify the auxiliary blower motor turn ON.
• If the auxiliary blower motor does not turn ON, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the auxiliary blower motor.
10. If all circuits test normal, test or replace the front auxiliary HVAC control assembly.
Blower Motor Malfunction
1. Ignition OFF, disconnect the appropriate blower motor relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal A2 and ground.
• If the test lamp illuminates, test the control circuit for a short to voltage.
3. Verify that a test lamp illuminates between the ignition circuit terminal C2 and ground.
• If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
4. Verify that a test lamp illuminates between the B+ circuit terminal C1 and ground.
• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
5. Connect a 30A fused jumper wire between the B+ circuit terminal C1 and the control circuit terminal A2. Verify the auxiliary blower motor turn ON.
• If the auxiliary blower motor does not turn ON, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the auxiliary blower motor resistor assembly.
6. Connect a test lamp between the ignition circuit terminal C2 and the control circuit terminal A1.
7. Cycle the front auxiliary HVAC control assembly blower motor switch between OFF and the appropriate speed position. The test lamp should turn ON and OFF when changing between the commanded states.
• If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the front auxiliary HVAC control assembly.
• If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the front auxiliary HVAC control assembly.
8. If all circuits test normal, test or replace the appropriate auxiliary blower motor relay.
Component Testing
Relay
1. Ignition OFF, disconnect the appropriate 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 B 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.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Auxiliary Heater and Air Conditioning Control Replacement - Front (Auxiliary Heater and Air Conditioning Control Replacement - Front)
* Auxiliary Blower Motor Replacement (Service and Repair)
* Auxiliary Blower Motor Resistor Assembly Replacement (Auxiliary Blower Motor Resistor Assembly Replacement)
* Auxiliary Blower Motor Relay Replacement (Service and Repair)