GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 1998 🢒 Silhouette Ext. 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 HVAC System Check

Step

Action

Normal Result(s)

Abnormal Result(s)*

1
  1. Install the scan tool.
  2. Turn the ignition switch to the RUN position.
  3. Select display DTC function with the scan tool.
  4. Check for any stored PCM or BCM DTCs related to HVAC operation.

No DTCs are stored in memory or current status.
    • DTC is stored in memory or current status (refer to appropriate DTC table).
    • Scan Tool Does Not Communicate. Refer to
      •  Scan Tool Inoperative

2
  1. Turn ignition to the OFF position.
  2. Remove the scan tool from the diagnostic link connector.
  3. Start the engine and allow the vehicle to idle in Park until the engine reaches operating temperature.
  4. Close the vehicle doors and windows.
  5. Engine decklid in the closed position.
  6. Turn the HVAC mode control knob to the instrument panel UPPER position.
  7. Turn the blower switch to position 3.
  8. Turn the temperature control knob to the maximum hot position.
  9. Press the A/C button so that it is in the OFF position.
  10. Press the OUTSIDE AIR button to the ON position.
  11. Install an accurate thermometer into the UPPER air outlet.
  1. Air flows from the instrument panel outlets.
  2. A/C is disengaged.
  3. Hot air is delivered to passenger compartment.
  4. Blower fan operates at medium speed.
  5. Delivered air temperature is approximately between 63°C and 68°C (145°F and 155°F) measured in typical garage settings (21°C to 24°C (70°F to 75°F)).
    • HVAC Compressor Clutch Does Not Disengage. Refer to HVAC Compressor Clutch Does Not Disengage .
    • Blower motor inoperative in one speed only (high speed operates normally-front). Refer to Blower Motor Inoperative in One Speed Only - Front High Speed Operates Normal
    • Temperature Control Inoperative. Refer to
    • Air Delivery Improper. Refer to Air Delivery Improper .
    • Heating Insufficient. Refer to Heating Insufficient .
    • Noise Diagnosis (Blower Motor). Refer to Noise Diagnosis - Blower Motor .

3
  1. Close all doors and windows.
  2. Engine decklid in the closed position.
  3. Turn the temperature control knob to the maximum cold position.
  4. Depress the A/C button to the ON position.
  5. Depress the RECIRC button.
  6. Turn the blower switch to position 3.
  7. Install a thermometer into the UPPER air outlet.
  1. Air flows from the instrument panel outlets.
  2. A/C light illuminates and compressor is engaged.
  3. Cold air is delivered to passenger compartment.
  4. Blower fan operates at medium speed.
  5. Delivered air temperature is approximately 18°C (30°F) lower than ambient temperature.
    • Noise Diagnosis (Blower Motor). Refer to Noise Diagnosis - Blower Motor .
    • Noise Diagnosis (A/C System). Refer to Noise Diagnosis - Air Conditioning (A/C) System .
    • Cooling Insufficient, A/C System. Refer to Cooling Insufficient - Air Conditioning (A/C) System .
    • HVAC Compressor Clutch Does Not Engage. Refer to HVAC Compressor Clutch Does Not Engage .
    • Blower motor inoperative in one speed only (high speed operates normally-front). Refer to Blower Motor Inoperative in One Speed Only - Front High Speed Operates Normal .
    • Temperature Control Inoperative. Refer to
    • Air Delivery Improper. Refer to Air Delivery Improper .

4
  1. Depress the A/C button to the OFF position.
  2. Depress the OUTSIDE AIR button.
  1. Air flows from the instrument panel outlets.
  2. A/C is disengaged.
  3. Outside air (ambient temperature) is delivered to passenger compartment.
  4. Blower fan continues to operate at moderate speed.
    • Noise Diagnosis (Blower Motor). Refer to Noise Diagnosis - Blower Motor .
    • Air Delivery Improper. Refer to Air Delivery Improper .
    • HVAC Compressor Clutch Does Not Disengage. Refer to HVAC Compressor Clutch Does Not Disengage .
    • Blower motor inoperative in one speed only (high speed operates normally-front). Refer to Blower Motor Inoperative in One Speed Only - Front High Speed Operates Normal .
    • Temperature Control Inoperative. Refer to

5
  1. Turn the HVAC mode control knob to the BI-LEVEL position.
  2. OUTSIDE AIR button is in the ON position.
  3. A/C button is in the OFF position.
  1. Air flows from the instrument panel outlets and floor outlets, slight air flow from the defrost outlets.
  2. A/C is disengaged.
  3. Outside air (ambient temperature) is delivered to passenger compartment.
  4. Blower fan continues to operate at moderate speed.
    • Noise Diagnosis (Blower Motor). Refer to Noise Diagnosis - Blower Motor .
    • Air Delivery Improper. Refer to Air Delivery Improper .
    • HVAC Compressor Clutch Does Not Disengage. Refer to HVAC Compressor Clutch Does Not Disengage .
    • Blower motor inoperative in one speed only (high speed operates normally-front). Refer to Blower Motor Inoperative in One Speed Only - Front High Speed Operates Normal .
    • Temperature Control Inoperative. Refer to

6
  1. Turn the HVAC mode control knob to the FLOOR position.
  2. Press the RECIRC button.
  3. A/C button is in the OFF position.
  1. Air flows from the floor outlets with slight air flow from the defrost outlets.
  2. A/C is disengaged.
  3. Recirculated air is delivered to passenger compartment.
  4. Blower fan continues to operate at moderate speed.
    • Noise Diagnosis (Blower Motor). Refer to Noise Diagnosis - Blower Motor .
    • Air Delivery Improper. Refer to Air Delivery Improper .
    • HVAC Compressor Clutch Does Not Disengage. Refer to HVAC Compressor Clutch Does Not Disengage .
    • Blower motor inoperative in one speed only (high speed operates normally-front). Refer to Blower Motor Inoperative in One Speed Only - Front High Speed Operates Normal .
    • Temperature Control Inoperative. Refer to

7

Turn the HVAC mode control knob to the DEFOG position.
  1. Air flows from the floor outlets and from the defrost outlets.
  2. OUTSIDE AIR light illuminates allowing outside air into vehicle to help clear windows.
  3. A/C is engaged.
  4. Cold air is delivered to passenger compartment.
  5. Blower fan continues to operate at moderate speed.
    • Noise Diagnosis (Blower Motor). Refer to Noise Diagnosis - Blower Motor .
    • Air Delivery Improper. Refer to Air Delivery Improper .
    • Noise Diagnosis (A/C System). Refer to Noise Diagnosis - Air Conditioning (A/C) System .
    • HVAC Compressor Clutch Does Not Engage. Refer to HVAC Compressor Clutch Does Not Engage .
    • Blower motor inoperative in one speed only (high speed operates normally-front). Refer to Blower Motor Inoperative in One Speed Only - Front High Speed Operates Normal .
    • Temperature Control Inoperative. Refer to

8

Turn the HVAC mode control knob to the DEFROST position.
  1. Air flows from the defrost outlets with slight air flow from the floor outlets.
  2. OUTSIDE AIR light illuminates allowing outside air into vehicle to help clear windows.
  3. A/C is engaged.
  4. Cold air is delivered to passenger compartment.
  5. Blower fan continues to operate at moderate speed.
    • HVAC Compressor Clutch Does Not Engage. Refer to HVAC Compressor Clutch Does Not Engage .
    • Blower motor inoperative in one speed only (high speed operates normally-front). Refer to Blower Motor Inoperative in One Speed Only - Front High Speed Operates Normal .
    • Temperature Control Inoperative. Refer to
    • Incorrect Air Distribution From Air Outlets. Refer to Air Delivery Improper .
    • Noise Diagnosis (Blower Motor). Refer to Noise Diagnosis - Blower Motor .
    • Air Delivery Improper. Refer to Air Delivery Improper .
    • Noise Diagnosis (A/C System). Refer to Noise Diagnosis - Air Conditioning (A/C) System .

9

Rotate the blower knob from OFF to position 5 and then back to OFF.

The blower motor speeds changes according to the blower switch position.
    • Blower motor inoperative at any speed (front). Refer to Blower Motor Inoperative at Any Speed from Front Heater Air Conditioning (A/C) Control Switch .
    • Blower motor high speed inoperative (front). Refer to Blower Motor High Speed Inoperative .
    • Blower motor operates continuously (front). Refer to Blower Motor Always On - Front .
    • Blower motor operates at high speed only (front). Refer to Blower Motor Operates at High Speed Only .
    • Blower motor inoperative in one speed only (high speed operates normally-front). Refer to Blower Motor Inoperative in One Speed Only - Front High Speed Operates Normal .

10

Turn the rear window wiper/washer and multi-function switch from OFF to positions 1, 2, and 3.

Rear blowers run at each position.

One rear blower motor speed inoperative. Refer to Blower Motor Inoperative in One Speed Only - from Rear Window Wiper/Washer and Multifunction Switch .

11
  1. Turn the rear window wiper/washer and multi-function switch to the REAR position.
  2. Turn the auxiliary heater-A/C control to positions 1, 2, and 3.

Rear blowers run at each position.
    • Auxiliary blower motor inoperative in one speed. Refer to Blower Motor Inoperative in One Speed Only - from Rear Aux Heater Air Conditioning (A/C) Control Switch .
    • Auxiliary blower motor totally inoperative from auxiliary heater-A/C control. Refer to Blower Motor Inoperative at Any Speed from Rear Aux Heater Air Conditioning (A/C) Control Switch .
    • Rear blower inoperative from rear window wiper/washer and multi-function switch. Refer to Blower Motor Inoperative at Any Speed from Rear Window Wiper/Washer and Multifunction Switch .

12

Turn the rear window wiper/washer and multi-function switch to the OFF position.

Rear blowers turn off.

Rear blowers always on (with ignition in RUN). Refer to Blower Motor Always On - Rear with Ignition in RUN .

* Refer to the appropriate symptom diagnostic table for the applicable abnormal result.