GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1998 🢒 Express 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 HVAC Air Delivery System Check

Step

Action

Normal Result(s)

Abnormal Result(s)*

1
  1. Start the vehicle engine.
  2. Allow vehicle to reach operating temperature.
  3. Place the blower switch in the high position.
  4. Place the temprature knob in the full heat (red) position.
  5. Place the mode knob in each of the following positions:
    6. • Defrost
    • Blend
    • Heater
    • Vent
  1. Blower motor will operate at high speed.
  2. Air temperature will be hot.
  3. Air flow in the defrost position is through the defrost outlets.
  4. Air flow in the blend position is through both defrost and heater outlets.
  5. Air flow in the heater position is through the heater outlets.
  6. Air flow in the vent position is through the A/C (vent) outlets.

Air flow does not change outlets.

Vacuum System

2
  1. Place the temperature knob in the full cold (blue) position.
  2. Place the mode knob in each of the following positions:
    3. • Defrost
    • Blend
    • Heater
    • Vent
  1. Blower motor will operate at high speed.
  2. Air flow will change to the appropriate outlets.
  3. Air temperature will be cooler.

Air temperature remains hot.

Temperature Actuator Inoperative

3

Place the mode knob in the following positions:

    • Max A/C
    • A/C
    • Bi-level
  1. Blower motor will operate at high speed.
  2. A/C compressor clutch will engage.
  3. Air temperature will be cold.
  4. Air flow in the Max A/C position is through the A/C (vent) outlets.
  5. Air flow in the A/C position is through the A/C (vent) outlets.
  6. Air flow in the Bi-level position is through both the A/C (vent) and heater outlets.

Air flow does not change outlets.

Vacuum System

Air temperature remains hot.

Temperature Actuator Inoperative

4

If vehicle is a cargo van equipped with an auxiliary HVAC unit preform the following steps:

  1. Place the front auxiliary HVAC control module blower switch in the high position.
  2. Place the mode knob in the lower position.
  3. Place the temperature knob in the full cold (blue) position.
  1. Auxiliary blower motor will operate at high speed.
  2. Air flow will be through the lower outlets of the auxiliary unit.
  3. Air temperature will be cold.

Temperature and Mode Valves Inoperative-Auxiliary .

Temperature Valve Assembly Inoperative - Auxiliary .

Mode Valve Only Inoperative - Auxiliary .

5
  1. Place the front auxiliary HVAC control module mode knob in the overhead position.
  2. Place the temperature knob in the full hot (red) position.
  1. Auxiliary blower motor will operate at high speed.
  2. Air flow will be through the overhead outlets of the auxiliary unit.
  3. Air temperature will be hot.

Temperature and Mode Valves Inoperative-Auxiliary .

Temperature Valve Assembly Inoperative - Auxiliary .

Mode Valve Only Inoperative - Auxiliary .

6

If vehicle is a passenger van equipped with an auxiliary HVAC unit preform the following steps:

Place the front auxiliary HVAC control module knobs in the following positions:

    • Blower switch in the high position.
    • Mode knob in the lower air delivery position.
    • Temperature knob in the full cold (blue) position.
  1. Auxiliary blower motor will operate at high speed.
  2. Air flow will be through the lower outlets of the auxiliary unit.
  3. Air temperature will be cold.

Temperature and Mode Valves Inoperative-Auxiliary .

Temperature Valve Assembly Inoperative - Auxiliary .

Mode Valve Only Inoperative - Auxiliary .

7
  1. Place the front auxiliary HVAC control module mode knob in the overhead air delivery position.
  2. Place the front auxiliary HVAC control module temperature knob in the full hot (red) position.
  1. Auxiliary blower motor will operate at high speed.
  2. Air flow will be through the overhead outlets of the auxiliary unit.
  3. Air temperature will be hot.

Temperature and Mode Valves Inoperative-Auxiliary .

Temperature Valve Assembly Inoperative - Auxiliary .

Mode Valve Only Inoperative - Auxiliary .

8
  1. Place the front auxiliary HVAC control module blower switch in the rear position.
  2. Place the rear auxiliary HVAC control module knobs in the following positions:
    3. • Blower switch in the high position.
    • Mode knob in the lower air delivery position.
    • Temperature knob in the full cold (blue) position.
  1. Auxiliary blower motor will operate at high speed.
  2. Air flow will be through the lower outlets of the auxiliary unit.
  3. Air temperature will be cold.

Temperature and Mode Valves Inoperative-Auxiliary .

Temperature Valve Assembly Inoperative - Auxiliary .

Mode Valve Only Inoperative - Auxiliary .

9
  1. Place the rear auxiliary HVAC control module mode knob in the overhead air delivery position.
  2. Place the rear auxiliary HVAC control module temperature knob in the full hot (red) position.
  1. Auxiliary blower motor will operate at high speed.
  2. Air flow will be through the overhead outlets of the auxiliary unit.
  3. Air temperature will be hot.

Temperature and Mode Valves Inoperative-Auxiliary .

Temperature Valve Assembly Inoperative - Auxiliary .

Mode Valve Only Inoperative - Auxiliary .

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