Diagnostic Aids
To prevent evaporator freezing, the recirc door periodically rotates back and forth from the outside air to recirc position. The tone of the blower and the velocity of the air speed may be noticeably different when the recirc actuator switches positions. This is a normal condition. If excessive air speed change is noticed inspect the cabin air filter for contamination or blockage.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step will determine if one or more blower speeds are inoperative.
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This step determines if the HVAC control module and blower motor control processor are attempting to control the blower motor speed.
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The measured voltage on the blower motor speed control circuit should steadily decrease from 4.75 V to 1.5 V as the blower speed is adjusted from the minimum speed position to the maximum speed position.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: HVAC Schematics Connector End View Reference: HVAC Connector End Views DEFINITION: The blower motor operates in at least one, but not all, speed positions. | ||||
1 | Did you perform the HVAC Diagnostic System Check? | -- | Go to Step 2 | |
Does the blower motor operate at the desired speed? | -- | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 3 | |
3 |
Does scan tool indicate that the Commanded Blower parameter increases within the specified range? | 10-100% | Go to Step 4 | Go to Step 10 |
Does the test lamp illuminate and increase intensity? | -- | Go to Step 8 | Go to Step 5 | |
5 | Test the battery positive voltage circuit and ground circuit of the blower motor control processor for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 6 |
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Important: Ensure that the blower motor control processor and HVAC control module connectors are connected during this step in order to avoid misdiagnosis.
Does the measured voltage decrease between the specified values? | 4.75-1.5 V | Go to Step 9 | Go to Step 7 | |
7 |
Does the voltage measure near the specified value? | 5.0 V | Go to Step 10 | Go to Step 9 |
8 | Inspect for poor connections at the harness connector of the blower motor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 11 |
9 | Inspect for poor connections at the harness connector of the blower motor control processor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 12 |
10 | Inspect for poor connections at the harness connector of the HVAC control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 13 |
11 | Replace the blower motor. Refer to Blower Motor Replacement in Heating, Ventilation and Air Conditioning. Did you complete the replacement? | -- | Go to Step 14 | -- |
12 | Replace the blower motor control processor. Refer to Blower Motor Control Processor Replacement Did you complete the replacement? | -- | Go to Step 14 | -- |
13 | Replace the HVAC control module. Refer to HVAC Control Module Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- |
14 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | Go to Step 2 |
