GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 1999 🢒 Cutlass 🢒 Engine 🢒 Engine Cooling 🢒 Heating Insufficient

Ambient Air Temperature

Heater Air Temperature

-18°C (0°F)

54°C (130°F)

-4°C (25°F)

59°C (139°F)

10°C (50°F)

64°C (147°F)

24°C (75°F)

68°C (155°F)

Step

Action

Value(s)

Yes

No

1
  1. Inspect the following items:
    2. • The coolant level
    • The belts
    • The belt tension. Refer to Drive Belt Tensioner Diagnosis in Engine Mechanical - 2.4L, or Drive Belt Tensioner Diagnosis in Engine Mechanical - 3.1L.
    • The surge tank cap
  2. Inspect the hoses for leaks or kinks.
  3. Adjust the heater control to the HEATER mode.
  4. Set the blower control to the HIGH position.
  5. Set the temperature control to the FULL HOT position.
  6. Turn the ignition switch to the ON position.
  7. Inspect for airflow out of the heater outlet.
  8. Inspect the outlet attachment.

Is the airflow high?

--

Go to Step 2

G to Step 20

2

Inspect the blower speeds for a change in the airflow.

Does the speed of the airflow change?

--

Go to Step 3

Go to HVAC Blower Controls System Check

3
  1. Adjust the heater control to the HEATER mode.
  2. Set the blower control to the HIGH position.
  3. Set the temperature control to the FULL HOT position.

    4. Caution: The cooling system is pressurized when hot.

  4. After the engine is sufficiently cool, remove the cooling system pressure cap.
  5. Start the engine. Idle the engine until the upper radiator hose is warm.
  6. Install the pressure cap.
  7. With the engine warm, drive the vehicle at 48 kph (30 mph). Ensure that the total warm up time equals 20 minutes.
  8. Use a thermometer in order to measure the ambient air temperature.
  9. Measure the discharge air temperature at the heater outlet.
  10. Compare the two temperatures to the above chart.

Is the heater temperature low according to the chart?

--

Go to Step 5

Go to Step 4

4
  1. Inspect the vehicle for air leaks at the following areas:
    2. • The dash
    • The heater cases
    • The vents
  2. Inspect under the seat for obstructions.
  3. Repair any leaks or obstructions as needed.

Does the problem persist?

--

Go to Step 5

System OK

5
  1. Turn the ignition switch to the ON position.
  2. Move the temperature control from the FULL COLD position to the FULL HOT position.
  3. Listen for the temperature valve operation.

Does the temperature valve appear to be operating?

--

Go to Step 6

Go to Step 17

6

Verify the temperature valve operation.

Is the temperature valve operating?

--

Go to Step 8

Go to Step 7

7

Inspect for the following conditions. Repair the components as needed.

    • A valve restriction
    • A valve disconnected from the temperature valve motor

Does the problem persist?

--

Go to Step 8

System OK

8
  1. Set the temperature control to the FULL HOT position.
  2. Start the vehicle.
  3. Warm the vehicle to operating temperature.
  4. Feel the inlet hose and the outlet hose.

Are both hoses warm?

--

Go to Step 9

Go to Step 12

9

Inspect the thermostat for the following conditions:

    • Proper installation
    • Proper seating
        Refer to Thermostat Diagnosis .

Is the installation OK?

--

Go to Step 10

Go to Step 11

10

Replace the thermostat. Refer to Engine Coolant Thermostat Replacement .

Is the repair complete?

--

System OK

--

11

Reinstall the thermostat. Refer to Engine Coolant Thermostat Replacement . Verify proper installation.

Is the repair complete?

--

System OK

--

12

Ensure that the outlet hose is hot and the inlet hose is warm.

  1. Remove the hoses at the heater core. Refer to Engine Coolant Thermostat Housing Replacement in Engine Cooling.
  2. Inspect for proper installation of the hoses.

Are the hoses installed in reverse?

--

Go to Step 13

Go to Step 14

13
  1. Properly install the hoses. Refer to Radiator Hose Replacement in Engine Cooling.
  2. Retest the system.

Does the problem persist?

--

Go to Step 14

System OK

14
  1. Backflush the heater core.
  2. Drain the engine coolant. Refer to Cooling System Draining and Filling in Engine Cooling.
  3. Replace the engine coolant. Refer to Cooling System Draining and Filling in Engine Cooling
  4. Retest the system.

Are both hoses warm?

--

Go to Step 15

Go to Step 16

15

Replace the heater core. Refer to Heater Core Replacement .

Is the repair complete?

--

System OK

--

16

Ensure that the outlet hose is hot and the inlet hose is warm.

Is the inlet hose hot and the outlet hose warm?

--

System OK

--

17

Inspect the connection to the temperature valve actuator.

Is the temperature valve actuator connected?

--

Go to Step 19

Go to Step 18

18

Connect the temperature valve actuator. Verify proper operation of the system.

Is the system operating properly?

--

System OK

--

19

Inspect the following components:

    • The actuator electrical circuit
    • The cable linkage

Repair or replace the components as needed.

Is the system operating properly?

--

System OK

--

20

The airflow is low or nonexistent.

Perform the HVAC functional inspection. Refer to VDOT Air Conditioning (A/C) System Diagnosis .

Does the problem persist?

--

Go to Step 21

System OK

21

Inspect the airflow out of the defroster outlets or the vent outlets.

Is the airflow out of the defroster outlets or the vent outlets high?

--

Go to Step 22

Go to Step 23

22

Inspect the system for the following conditions:

    • A restricted heater defroster valve
    • A restricted mode valve

Repair or replace the valves as needed. Refer to Floor Air Outlet Replacement .

Is the repair complete?

--

System OK

--

23

The airflow out of the defroster outlets or the vent outlets is low or nonexistent.

  1. Switch the mode to DEFROSTER.
  2. Inspect the airflow.

Is the defroster airflow OK?

--

Go to Step 24

Go to Step 25

24
  1. Remove the heater outlet. Refer to Floor Air Outlet Replacement .
  2. Inspect the heater for obstructions.
  3. Remove any obstructions as needed.

Does the system operate properly?

--

System OK

--

25

Inspect the blower speeds for airflow changes.

Are the speed changes OK?

--

Go to Step 26

Go to HVAC Blower Controls System Check

26

Inspect the system for obstructions at the blower inlet and the plenum.

Were any obstructions found?

--

Go to Step 27

Go to Step 28

27

Remove the obstructions as needed.

Does the system operate properly?

--

System OK

--

28
  1. Set the blower to the HIGH position.
  2. Move the temperature control from the FULL HOT position to the FULL COLD position.
  3. Listen for a change in the air flow.

Did a change in the airflow occur?

--

Go to Step 29

Go to Step 30

29

Inspect the system for an obstruction between the blower and the system outlets. Remove any obstruction as needed.

Does the system operate properly?

--

System OK

--

30

Inspect the temperature valve and the actuator for proper operation. Repair the components as needed.

Does the system operate properly?

--

System OK

--