For 1990-2009 cars

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: HVAC Schematics DEFINITION: The temperature cannot be adjusted or the heating is insufficient.
1 | Did you review the HVAC operation and perform the necessary inspections? | -- | Go to Step 2 | Go to Symptoms - HVAC Systems - Manual
2 | Does the blower actuator operate correctly for each speed position? | -- | Go to Step 3 | Go to Blower Motor Malfunction
3 | Is the HVAC control assembly inoperative? | -- | Go to Step 16 | Go to Step 4
4 | Inspect the cooling system for the following:

• | A low coolant level

• | A loose or worn accessory drive belt

• | Leaking radiator hoses or leaking heater hoses

• | Kinked radiator hoses or kinked heater hoses

• | A missing radiator cap pressure seal

• | A leaking radiator cap

Did you find and correct the condition?

--

Go to Step 20

Go to Step 5

5 |

1. Start the engine.
2. Place the blower motor switch in the OFF position.
3. Place the A/C request switch in the OFF position.

Does the A/C compressor operate?

--

Go to Air Conditioning Compressor Malfunction

Go to Step 6

6 |

1. Observe the drive shaft of both air temperature actuators.
2. Adjust the air temperature switch.

Does the drive shaft of both air temperature actuators rotate?

--

Go to Step 7

Go to Step 8

7 | Inspect the appropriate air temperature door and the appropriate air temperature door actuator for the following conditions:

• | A misaligned actuator on the air temperature door

• | Broken linkages or binding linkages

• | A broken air temperature door or a binding air temperature door

• | An obstruction that prevents the air temperature door from operating within the full range of motion

• | Missing seals to the air temperature door

• | Misaligned seals to the air temperature door

Did you find and correct the condition?

--

Go to Step 20

Go to Heating Performance Diagnostic

8 | Test the position signal circuit of the appropriate temperature actuator for an open or for a high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 9
9 | Test the low reference circuit of the appropriate temperature actuator for an open or for a high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 10
10 | Test the 5-volt reference circuit of the appropriate air temperature actuator for a high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 11
11 |

1. Turn OFF the ignition.
2. Reconnect the appropriate temperature actuator.
3. Turn ON the ignition with the engine OFF.
4. Connect a test lamp between temperature door control A and temperature door control B circuits of the appropriate temperature actuator connector.
5. Place the temperature switch in the cold position.
6. Place the temperature switch in the hot position.

Does the test lamp illuminate in both positions?

--

Go to Step 20

Go to Step 12

12 | Test the temperature door control A and temperature door control B circuits of the appropriate temperature actuator for an open, a high resistance, a short to ground, or a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 13
13 | Test the ignition 3 voltage circuit of the HVAC control module for an open or for a high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 16
14 | Test the ground circuit of the HVAC control module for an open or for a high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? |  | Go to Step 15 | Go to Step 17
15 | Inspect the appropriate air temperature door for a mechanical condition or for a condition that allows excessive travel of the door. Did you complete the repair? | -- | Go to Step 20 | --
16 | Inspect for poor connections at the harness connector of the appropriate air temperature actuator. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 18
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 . Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 19
18 | Important: Perform the calibration procedure for the air temperature actuator. Replace the appropriate air temperature door actuator. Refer to Temperature Valve Actuator Replacement - Right Side Temperature Valve Actuator Replacement - Left Side .

Did you complete the replacement?

--

Go to Step 20

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19 | Replace the HVAC control module. Refer to Heater and Air Conditioning Control Replacement . Did you complete the replacement? | -- | Go to Step 20 | --
20 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | Go to Step 2