Air Delivery Improper

Air Delivery Improper

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 HVAC control assembly uses vacuum to control the mode doors. Vehicles equipped with diesel engines use a vacuum pump to create vacuum. The vacuum pump has ignition voltage circuit and a ground circuit to operate. The pump turns on when vacuum is low and turns off when vacuum reaches 21 Hg.

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

1. Ignition ON, mode set to the VENT position, place the blower switch in the LO, MED 1, MED 2 and HI speed positions. The blower motor should activate and operate from low to medium 1, medium 2, to high when changing between the commanded states.

• If the blower motor speed does not change or fails to operate at a selected speed, refer to Blower Motor Malfunction (Blower Motor Malfunction).

2. Rotate the mode control switch from the OFF position to the VENT, BI-LEVEL, FLOOR, FLOOR/DEFROST and DEFROST positions. The air flow should follow the commanded states and blow through the vent, floor and defrost outlets.

• If the air flow fails to blow through the selected outlets, refer to Vacuum Control System Diagnostic (Vacuum Control System Diagnostic).

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the vacuum pump.
2. Test for less than 1.0 ohm between the ground circuit terminal A 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 circuit terminal B and ground.

• If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.

4. If all circuits test normal, test or replace the vacuum pump assembly.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

Vacuum Pump Assembly Replacement (HVAC - Manual)