Too Cold in Vehicle - Auxiliary. GMC Truck GMC C Sierra

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C Sierra - 2WD 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 Too Cold in Vehicle - Auxiliary

Too Cold in Vehicle - Auxiliary with Sunroof

Test Description

The numbers below refer to thew step numbers on the diagnostic table.

This step ensures that the primary HVAC system is functioning properly.

If the condition does not occur when a heating request has been made then you must bypass the A/C compressor and cooling system diagnostic information.

Step

Action

Values

Yes

Schematic Reference: HVAC Schematics

DEFINITION: Auxiliary air temperature cannot be adjusted or auxiliary heating is insufficient.

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

Go to Step 2

Go to Symptoms - HVAC Systems - Manual

Important:: The auxiliary HVAC control assembly operates independently of the HVAC control module to provide heated airflow through the auxiliary system.

Does the HVAC control module operate and provide sufficient heating?

Go to Step 3

Go to Too Cold in Vehicle

Turn ON the ignition, with the engine OFF.
Place the A/C auxiliary blower motor switch in each speed position.

Does the auxiliary blower motor operate at all?

Go to Step 4

Go to Auxiliary Blower Motor Inoperative

Does the auxiliary blower motor operate correctly for each speed position?

Go to Step 5

Go to Auxiliary Blower Motor Malfunction

Inspect the cooling system for the following conditions:

•	A low coolant level

•	A loose or worn accessory drive belt

•	A leaking radiator or auxiliary heater hoses

•	A kinked radiator or auxiliary heater hoses

•	A missing radiator cap pressure seal

•	A leaking radiator cap

Did you find and correct the condition?

Go to Step 18

Go to Step 6

Start the engine.
Place the blower motor switch in the OFF position.
Place the A/C request switch in the OFF position.

Does the A/C compressor operate?

Go to HVAC Compressor Clutch Does Not Disengage

Go to Step 7

Turn ON the ignition, with the engine OFF.
Observe the drive shaft of the auxiliary air temperature actuator.
Adjust the auxiliary air temperature switch.

Does the auxiliary air temperature actuator drive shaft rotate at all?

Go to Step 8

Go to Step 9

Inspect the auxiliary air temperature door and the auxiliary air temperature actuator for the following conditions:

•	Misaligned auxiliary air temperature actuator. Refer to Auxiliary Temperature Valve Actuator Replacement .

•	Broken or binding linkages or auxiliary air temperature door

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

•	Missing seals to the auxiliary air temperature door

•	Misaligned seals to the auxiliary air temperature door

Did you find and correct the condition?

Go to Step 18

Go to Heating Performance Diagnostic

Test the ignition 3 voltage circuit of the auxiliary air temperature 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 18

Go to Step 10

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

Did you find and correct the condition?

Go to Step 18

Go to Step 11

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

Did you find and correct the condition?

Go to Step 18

Go to Step 12

Important:: The auxiliary HVAC control assembly connector must be connected to correctly perform test.

Turn ON the ignition, with the engine OFF.
Measure the voltage from the auxiliary temperature door control circuit of the auxiliary air temperature actuator to a good ground.
Adjust the auxiliary air temperature switch.

Does the voltage change and measure within the specified range?

0-12 V

Go to Step 13

Go to Step 15

Inspect for poor connections at the harness connector of the auxiliary air temperature 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 18

Go to Step 14

Inspect the auxiliary air temperature actuator, door and any attaching linkage for binding or a condition that prevents drive shaft rotation

Did you find and correct the condition?

Go to Step 18

Go to Step 16

Inspect for poor connections at the harness connector of the auxiliary 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 18

Go to Step 17

Replace the auxiliary air temperature actuator. Refer to Air Temperature Actuator Replacement .

Did you complete the replacement?

Go to Step 18

Replace the auxiliary HVAC control assembly. Refer to Auxiliary Heater and Air Conditioning Control Replacement - Front .

Did you complete the replacement?

Go to Step 18

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2

Too Cold in Vehicle - Auxiliary w/o Sunroof

Test Description

The numbers below refer to the step numbers on the diagnostic table.

This step ensures that the primary HVAC system is functioning properly.

If the condition does not occur when a heating request has been made then you must bypass the A/C compressor and cooling system diagnostic information.

This step ensures that the rear auxiliary HVAC control module is able to move the auxiliary air temperature actuator.

This step ensures that the front auxiliary HVAC control assembly is able to move the auxiliary air temperature actuator.

The circuit that is to be tested runs between the rear auxiliary HVAC control assembly and the auxiliary HVAC control processor. The circuit is the position signal from the rear auxiliary HVAC control assembly for the auxiliary air temperature actuator. The circuit only provides a reference when the front auxiliary HVAC control assembly is in the REAR CNTL position.

The circuit that is to be tested runs between the front auxiliary HVAC control assembly and the auxiliary HVAC control processor. The circuit is the position signal from the rear auxiliary HVAC control assembly for the auxiliary air temperature actuator. The circuit only provides a reference when the front auxiliary HVAC control assembly is in any other position than REAR CNTL position.

This step checks the output of the auxiliary HVAC control processor to the auxiliary air temperature actuator.

Step

Action

Values

Yes

Schematic Reference: HVAC Schematics

DEFINITION: Auxiliary air temperature cannot be adjusted from one or both auxiliary controls or auxiliary heating is insufficient.

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

Go to Step 2

Go to Symptoms - HVAC Systems - Manual

Important:: The auxiliary HVAC control assembly operates independently of the HVAC control module to provide heated airflow through the auxiliary system.

Does the HVAC control module operate and provide sufficient heating?

Go to Step 3

Go to Too Cold in Vehicle

Turn ON the ignition, with the engine OFF.
Select REAR CNTL on the front auxiliary HVAC control assembly.
Place the A/C auxiliary blower motor switch in each speed position.

Does the auxiliary blower motor operate at all?

Go to Step 4

Go to Auxiliary Blower Motor Inoperative

Does the auxiliary blower motor operate at the desired speed in each speed position?

Go to Step 5

Go to Auxiliary Blower Motor Malfunction

Inspect the cooling system for the following conditions:

•	A low coolant level

•	A loose or worn accessory drive belt

•	A leaking radiator or auxiliary heater hoses

•	A kinked radiator or auxiliary heater hoses

•	A missing radiator cap pressure seal

•	A leaking radiator cap

Did you find and correct the condition?