Blower Motor Malfunction
Blower Motor Malfunction
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 HVAC control module applies voltage to the 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 blower motor per particular speed request:
* Low speed - 4 resistors
* Medium 1 speed - 3 resistors
* Medium 2 speed - 2 resistors
* Medium 3 speed - 1 resistor
When the operator requests High speed, the HVAC control module applies voltage to the blower motor relay through the high blower motor control circuit. The voltage energizes the blower motor relay, connecting the blower motor to battery positive voltage.
Circuit/System Verification
Listen to the function of the blower motor while commanding the blower motor speed from Off through to the High speed positions using the blower motor switch, the blower motor speed should increase and decrease speeds when changing between the speed positions.
If the blower motor speed does not change, refer to Blower Motor Malfunction.
Circuit/System Testing
Blower Motor Malfunction
1. Ignition OFF, disconnect the harness connector at the blower motor resistor assembly.
2. While changing the fan speed switch between the Low, M1, M2, M3 and High positions, verify that a test lamp illuminates between ground and the appropriate blower motor control circuit terminals listed below:
* Low terminal D
* M1 terminal C
* M2 terminal B
* M3 terminal A
* High terminal F
^ If the test lamp does not illuminate, test the appropriate control circuit for a short to ground or an open/high resistance.
3. Ignition OFF, connect the harness connector at the blower motor resistor assembly and disconnect the blower motor.
4. Ignition ON, connect a test lamp between the blower motor control circuit terminal A and the blower motor ground circuit terminal B.
5. Cycle the fan speed switch between the Low, M1, M2, M3 and High positions. 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, 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, replace the blower motor resistor assembly.
6. If all circuits test normal, test or replace the blower motor.
Component Testing
Blower Motor Test
1. Ignition OFF, disconnect the harness connector at the 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 control circuit terminal A and ground. Verify the blower motor activates.
^ If the blower motor does not activate, replace the blower motor.
Relay Test
1. Ignition OFF, disconnect the HVAC BLOWER HIGH relay.
2. Test for 60-200 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 less than infinite resistance, replace the relay.
4. Test for less than 2 ohms between terminals 30 and 87A.
^ If greater than 2 ohms, replace the relay.
5. Install a 3-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Measure for less than 2 ohms between terminals 30 and 87.
^ If greater than 2 ohms, replace the relay.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
* Blower Motor Resistor Assembly Replacement
* Blower Motor Replacement