GM Service Manual Online
For 1990-2009 cars only

Step

Action

Value(s)

Yes

No

Schematic Reference: HVAC Schematics

DEFINITION: The temperature cannot be adjusted, or the cooling is insufficient during A/C operation.

1

Did you perform the HVAC Diagnostic System Check?

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Go to Step 2

Go to Diagnostic System Check - HVAC Systems - Automatic

2

Important:: The RDO-BATT fuse must be removed for 20 seconds minimum. The HVAC control module requires 60 seconds to initialize after the HVAC fuse is reinstalled. Do not install a scan tool during this time.

  1. Disconnect the scan tool.
  2. Turn OFF the ignition.
  3. Remove the RDO-BATT fuse to interrupt the keep alive memory of the HVAC control module.
  4. Install the RDO-BATT fuse.
  5. Install a scan tool.
  6. Turn ON the ignition, with the engine OFF.
  7. Observe the current DTC list in Heating, Ventilation and Air Conditioning using the scan tool.

Does the scan tool display DTC B0408, B0415 or B0416?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3

Place the blower motor switch in each speed position.

Does the blower motor operate in each speed position?

--

Go to Step  4

Go to Blower Motor Inoperative

4

Does the blower motor provide sufficient air flow?

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Go to Step  5

Go to Blower Motor Malfunction

5

  1. Place the recirculation switch in the ON position.
  2. Observe the recirculation door.
  3. Place the outside air switch in the ON position.

Does the Recirculation Door operate properly?

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Go to Step 6

Go to Air Delivery Improper

6

Does the Too Hot in Vehicle concern occur when A/C cooling is desired?

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Go to Step  7

Go to Step 9

7

Important:: Ambient air temperature must be above 3°C (38°F).

  1. Cover the Sunload Sensor.
  2. Start the engine.
  3. Open all panel outlets to allow maximum air flow.
  4. Place the air temperature switch in the coldest position.
  5. Place the mode switch in the vent position.
  6. Place the blower motor switch in the maximum speed position.
  7. Place the recirculation switch in the ON position.

Is the A/C compressor ON?

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Go to Step  8

Go to HVAC Compressor Clutch Does Not Engage

8

Perform the refrigerant system performance test. Refer to Air Conditioning (A/C) System Performance Test in Heating, Ventilation and Air Conditioning.

Are the low and high side pressure values within the allowable limits for the recorded ambient air temperature, and within 103 kPa (15 psi) of each other?

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Go to Step  9

Go to Leak Testing in Heating, Ventilation and Air Conditioning

9

Check the upper discharge, lower air temperature, and inside air temperature sensors for proper installation. Refer to Upper Discharge Air Temperature Sensor Replacement , Air Temperature Sensor Replacement - Lower , Inside Air Temperature Sensor Replacement .

Did you find and correct the condition?

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Go to Step  21

Go to Step  10

10

  1. Install a scan tool.
  2. Inspect for airflow through the inside air temperature sensor by placing a 5 cm (2 in) square piece of paper over the sensor air inlet.

Does the paper stay in place?

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Go to Step  11

Go to Step  15

11

  1. Install a thermometer near the upper outlet, lower outlet and inside air temperature sensors.
  2. With a scan tool, observe the Upper Outlet, Lower Outlet and Inside Air Temp data parameters in the Heating and A/C Data list.

Do the temperatures vary by more than the specified range?

-3 to +3°C

(-5 to +5°F)

Go to Step  12

Go to Step  14

12

  1. Turn the engine OFF.
  2. Install a scan tool.
  3. Cover the sunload sensor.
  4. Start the engine.
  5. Adjust driver side temperature to 22°C (72°F).
  6. With a scan tool, observe the Solar Sensor data parameter in the Heating and Air Conditioning data list.

Does the scan tool indicate that the solar sensor parameter is greater than the specified value?

230 counts

Go to Step  13

Go to Step  16

13

  1. Uncover the sunload sensor.
  2. Direct a light source at the sunload sensor.

Do the counts change?

--

System OK

Go to Step  16

14

Test the suspect temperature sensor resistance. Refer to Sensor Resistance Table .

Does the resistance measure near the Sensor Resistance Table?

--

Go to Step  17

Go to Step 15

15

Inspect for poor connections at the harness connector of the suspect air temperature sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

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Go to Step  21

Go to Step  18

16

Inspect for poor connections at the harness connector of the sunload sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

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Go to Step  21

Go to Step  19

17

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?

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Go to Step  21

Go to Step  20

18

Replace the temperature sensor. Refer to Inside Air Temperature Sensor Replacement , Upper Discharge Air Temperature Sensor Replacement or Air Temperature Sensor Replacement - Lower .

Did you complete the replacement?

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Go to Step  21

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19

Replace the sunload sensor. Refer to Sun Load Sensor Replacement .

Did you complete the replacement?

--

Go to Step 21

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20

Important: Perform the recalibration procedure for the HVAC control module.

Replace the HVAC control module. Refer to HVAC Control Module Replacement .

Did you complete the replacement?

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Go to Step  21

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21

Operate the system in order to verify the repair.

Did you correct the condition?

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System OK

Go to Step 3