For 1990-2009 cars

### Circuit Description

When the A/C switch is pressed on the heater and A/C control, an internal timer begins counting the amount of time the A/C switch is being depressed. The timer stops counting when the switch is released.

### Conditions for Running the DTC

The diagnostic runs every 40 ms.

### Conditions for Setting the DTC

The A/C switch is active for at least 15 counts.

### Action Taken When the DTC Sets

The DTC is stored in memory.

### Conditions for Clearing the DTC

The DTC clears after 20 fault-free ignition cycles.

#### DTC 37 - Heater and A/C Control Switch Stuck

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 |

1. Install the scan tool.
2. Select A/C SWITCH from the data list.
3. Monitor the scan tool and press the A/C button, on the heater and A/C control, ON and OFF several times.

Does the scan tool display ACTIVE and INACTIVE while pressing the button?

--

Go to Step 2

Go to Step 3

2 |

1. Using the scan tool, clear codes.
2. Recycle the ignition switch ending in the ON position.
3. Press the A/C switch ON and OFF several times.
4. Recheck for a current DTC 37.

Is a current DTC 37 present?

--

Go to Step 4

System OK

3 | Did the scan tool display ACTIVE at all times? | -- | Go to Step 4 | Go to Step 5
4 |

1. Replace the heater and A/C control.
2. Use the scan tool in order to program the new controller.

Did you complete the replacement?

--

Go to Step 6

--

5 |

1. Condition is intermittent at this time.
2. Use the scan tool in order to clear codes.
3. Verify that all functions on the controller operate properly and return vehicle to owner.
4. If this DTC continues to reset later on a consistent basis, replace the controller.

Did you complete this action?

--

System OK

--

6 | Verify that all the HVAC functions operate properly. Is the HVAC system operating properly? | -- | System OK | --