Auxiliary Blower Motor Malfunction (RPO C69 with Rear Controls)
Auxiliary Blower Motor Malfunction (RPO C69 with Rear Controls)
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
The auxiliary HVAC control processor controls all outputs for the auxiliary HVAC system. The auxiliary HVAC control processor receives inputs from the front and rear auxiliary HVAC control assemblies. The auxiliary HVAC control processor does not utilize Class 2 communications. The auxiliary HVAC control processor monitors the front auxiliary blower motor switch control circuit, when the auxiliary blower motor speed control is set to REAR, the voltage potential of the circuit drops to zero, when the auxiliary HVAC control processor senses the voltage drop, it will enable the rear auxiliary HVAC control.
The auxiliary blower motor switch 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.
Circuit/System Verification
1. Ignition ON, command the auxiliary blower motor to operate in the LOW, MED and HIGH modes by using the auxiliary blower switch in the front auxiliary HVAC control assembly. The auxiliary blower motor speed should vary in each speed position.
^ If the auxiliary blower motor is inoperative at all speeds, refer to Blower Motor Inoperative.
^ If the auxiliary blower motor functions at a single speed only, refer to Blower Motor Malfunction.
2. Place the auxiliary blower switch in the REAR position and command the auxiliary blower motor to operate in the LOW, MED and HIGH modes from the rear auxiliary HVAC control. The auxiliary blower motor speed should vary in each speed position.
^ If the auxiliary blower motor is inoperative from the rear auxiliary HVAC control, refer to Rear Auxiliary HVAC Control 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 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.
3. Ignition OFF, connect the harness connector at the front auxiliary HVAC control assembly and disconnect the auxiliary high speed blower motor relay.
4. 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.
5. 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 or replace the auxiliary high speed blower motor relay.
6. 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 control circuit terminal A2 for a short to ground.
7. Disconnect the harness connector at the auxiliary blower motor.
8. Test for less than 1.0 ohm between the auxiliary blower motor ground circuit terminal A and ground
^ If greater than the specified range, test the ground circuit for an open/high resistance.
9. Connect the harness connector at the auxiliary blower motor.
10. Connect a 30A fused jumper wire between the B+ circuit terminal C1 and the control circuit terminal A2. Verify the auxiliary blower motor is activated.
^ If the auxiliary blower motor does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the auxiliary blower motor.
11. Connect a test lamp between the ignition circuit terminal C2 and the control circuit terminal A1.
12. Command the auxiliary blower motor to operate from HIGH to OFF by using the auxiliary blower motor switch. 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 auxiliary blower motor switch.
^ 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 auxiliary blower motor switch.
13. If all circuits test normal, test or replace the auxiliary high speed blower motor relay.
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. If the circuit tests normal and the ignition circuit fuse is open, test or replace the appropriate blower motor relay.
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. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit terminal A2 for a short to ground.
5. Connect a 30A fused jumper wire between the B+ circuit terminal C1 and the control circuit terminal A2. Verify the auxiliary blower motor is activated.
^ If the auxiliary blower motor does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, 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. Command the auxiliary blower motor to operate from OFF to LOW to MED by using the auxiliary blower motor switch. 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 auxiliary blower motor switch.
^ 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 auxiliary blower motor switch.
8. If all circuits test normal, test or replace the appropriate blower motor relay.
Rear Auxiliary HVAC Control Malfunction
1. Ignition OFF, disconnect the harness connector at the auxiliary HVAC control processor.
2. Test for less than 1.0 ohm at the ground circuit terminal H and ground.
^ If greater than the specified range, test the ground circuit for an open/high resistance.
3. Ignition ON verify that a test lamp illuminates between the ignition 3 voltage terminal J and ground.
^ If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
4. Connect a test lamp between the front auxiliary blower motor switch control terminal M and ground.
5. Command the auxiliary blower motor switch control ON and OFF by switching the front auxiliary blower motor switch from REAR to OFF. 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 voltage, 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 ground or an open/high resistance. If the circuit tests normal, replace the front auxiliary HVAC control assembly.
6. Connect a test lamp between the rear auxiliary blower motor switch control circuit terminal L and ground.
7. Command the auxiliary blower motor to operate by using the rear auxiliary blower motor switch from OFF, to LOW, MED and HIGH. The test lamp should illuminate when commanding the LOW, MED and HIGH states.
^ If the test lamp is always OFF, test the control circuit for a short to ground or and open/high resistance. If the circuit tests normal, replace the rear auxiliary HVAC control assembly.
^ If the test lamp is always ON test the control circuit for a short to voltage. If the circuit tests normal, replace the rear auxiliary HVAC control assembly.
8. If all circuits test normal, replace the auxiliary HVAC control processor.
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 after completing the diagnostic procedure. Verification Tests
* Auxiliary HVAC Control Processor Replacement
* Auxiliary Blower Motor Switch Replacement
* Relay Replacement (Attached to Wire Harness) Relay Replacement (Within an Electrical Center)
* Auxiliary Heater and Air Conditioning Control Replacement - Rear
* Auxiliary Heater and Air Conditioning Control Replacement - Front
* Auxiliary Blower Motor Replacement
* Auxiliary Blower Motor Resistor Assembly Replacement.