Air Delivery Improper. GMC Truck GMC C Sierra

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C Sierra - 2WD 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 Air Delivery Improper

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

This step tests for a blower motor that does not operate regardless of the desired blower motor speed.

This step tests for a blower motor that operates, yet does not accurately respond to the desired blower motor speed.

This step verifies that there is power to the HVAC control assembly.

The voltage will vary between 0-5 volts during normal operation. The HVAC control assembly connector must be connected during this step.

Step

Action

Value(s)

Yes

Schematic Reference: HVAC Schematics

DEFINITION: Air does not flow correctly from the air distribution outlets.

Did you review the HVAC operation and perform the necessary inspections?

Go to Step 2

Go to Symptoms - HVAC Systems - Manual

Turn ON the ignition, with the engine OFF.
Place the blower control in the OFF position.

Is the blower motor OFF?

Go to Step 3

Go to Blower Motor Always On

Place the blower control in each speed position.

Does the blower motor operate at all?

Go to Step 4

Go to Blower Motor Inoperative

Does the blower motor operate correctly for each speed position?

Go to Step 5

Go to Blower Motor Malfunction

Is the HVAC control assembly inoperative in all positions?

Go to Step 6

Go to Step 16

Observe the mode actuator drive shaft.
Place the mode control in each mode position.

Does the mode actuator drive shaft rotate for each selected position?

Go to Step 7

Go to Step 8

Inspect the mode door and the mode actuator for the following:

•	Incorrectly installed mode actuator

•	Broken or binding linkages or mode door

•	Obstruction that prevents the mode door from operating within it's full range of motion

Did you find and correct the condition?

Go to Step 23

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Test the ignition 3 voltage circuit of the mode actuator for an open or a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 23

Go to Step 9

Test the ground circuit of the mode actuator for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 23

Go to Step 10

Test the 5 volt reference circuit of the mode actuator for an open, a high resistance, short to ground, or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 23

Go to Step 11

Test the mode door position signal circuit of the mode actuator for an open, a high resistance, short to ground, or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 23

Go to Step 12

Test the mode door control circuit of the mode actuator for an open, a high resistance, short to ground, or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 23

Go to Step 13

Important: The mode actuator connector and the HVAC controller connector must be connected to correctly perform the test.

Turn ON the ignition, with the engine OFF.
Backprobe and monitor the voltage from the mode door position signal circuit of the mode actuator to a good ground.
Connect a 3 amp fused jumper wire between the mode door control circuit and the 5 volt reference circuit of the mode actuator (drives the motor to FLR).
Remove and reconnect the jumper wire between the mode door control circuit and the ground circuit of the mode actuator (drives the motor to DEF).

Does the mode actuator drive shaft rotate and does the voltage change?

Go to Step 14

Go to Step 18

Backprobe the mode actuator connector terminal in order to measure the voltage from the mode door control circuit to a good ground.
Place the mode control in each mode position.

Does the voltage measure near the specified value when airflow moves toward DEF, near the specified value when airflow moves toward FLR, and near the specified value when stationary?

0 V toward DEF

5 V toward FLR

2.5 V stationary

Go to Step 15

Go to Step 20

Inspect the mode door for a mechanical failure or a condition that allows excessive travel to the door.

Did you find and correct the condition?

Go to Step 23

Test the ignition 3 voltage circuit of the HVAC controller for an open, a high resistance or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 23

Go to Step 17

Test the ground circuit of the HVAC controller for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 23

Go to Step 20

Inspect for poor connections at the harness connector of the mode actuator. 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 23

Go to Step 19

Inspect the mode door and any attaching linkage for any binding.
Inspect the ductwork for any debris that would prevent air flow through the ductwork.

Did you find and correct the condition?

Go to Step 23

Go to Step 21

Inspect for poor connections at the harness connector of the HVAC control assembly. 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 23

Go to Step 22

Replace the mode actuator. Refer to Mode Actuator Replacement .

Did you complete the replacement?

Go to Step 23

Replace the HVAC control assembly. Refer to Heater and Air Conditioning Control Replacement .

Did you complete the replacement?

Go to Step 23

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2