For 1990-2009 cars

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 | Yes | No
--- | --- | --- | ---
1 |

1. Inspect the following items:

• | The coolant level

• | The belts

• | The belt tension

• | 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

Go to Step 14

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. 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 and the discharge air temperature at the heater outlet.
9. Compare the temperatures to the above table.

Is the heater temperature low according to the table?

Go to Step 5

Go to Step 4

4 |

1. Inspect the vehicle for air leaks at the following areas:

• | The dash

• | The heater cases

• | The vents

2. Inspect under the seat for obstructions.
3. Repair any leaks or obstructions as needed.

Does the condition 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. Inspect the temperature control cable for operating.

Does the temperature control cable operate the temperature valve?

Go to Step 6

Go to Step 12

6 |

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 heater hose and the outlet heater hose.

Are both hoses warm?

Go to Thermostat Diagnosis in Engine Cooling

Go to Step 7

7 | The outlet hose is hot and the inlet hose is warm.

1. Remove the hoses at the heater core.
2. Inspect for proper installation of the hoses.

Are the hoses installed in reverse?

Go to Step 8

Go to Step 9

8 |

1. Properly install the hoses.
2. Retest the system.

Does the condition persist?

Go to Step 9

System OK

9 |

1. Drain the engine coolant.
2. Backflush the heater core.
3. Replace the engine coolant.
4. Retest the system.

Are both hoses warm?

Go to Step 10

Go to Step 11

10 | Replace the heater core. Refer to Heater Core Replacement . Is the repair complete? | System OK | --
11 | Is the inlet hose hot and the outlet hose warm? | System OK | --
12 | Inspect the temperature valve operation. Is the temperature valve operating? | System OK | Go to Step 13
13 | Inspect the temperature actuator for operating. Refer to Temperature Actuator Inoperative . Is the system operating properly? | System OK | --
14 | The airflow is low or nonexistent. Perform the HVAC functional inspection. Refer to Functional Check Does the condition persist? | Go to Step 15 | System OK
15 | Inspect the airflow out of the following outlets:

• | The defroster outlets

• | The vent outlets

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

Go to Step 16

Go to Step 17

16 |

1. Inspect for the following conditions:

• | A restricted heater defroster valve

• | A restricted mode valve

2. Repair or replace the valves as needed.

Is the repair complete?

System OK

--

17 | 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 18

Go to Step 19

18 |

1. Remove the heater outlet.
2. Inspect the heater for obstructions.
3. Remove any obstructions as needed.

Does the system operate properly?

System OK

--

19 | Inspect the blower speeds for airflow changes. Are the speed changes OK? | Go to Step 20 | Go to HVAC Blower Controls System Check
20 | Inspect the system for obstructions at the blower inlet and the plenum. Did you find any obstructions? | Go to Step 21 | Go to Step 22
21 | Remove the obstructions as needed. Does the system operate properly? | System OK | --
22 |

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 23

Go to Step 24

23 |

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

Does the system operate properly?

System OK

--

24 |

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

Does the system operate properly?

System OK

--