Ambient Temperature Sensor / Switch HVAC: Testing and Inspection

There are two failure modes possible for the Ambient Temperature Sensor:
1. Short Circuit - The temperature blend door will be biased toward cooler than the set position of the temperature lever. Movement of the temperature lever will provide some temperature modulation.
2. Open Circuit - The temperature blend door will be biased toward warmer than the set position of the temperature lever. Movement of the temperature lever will provide some temperature modulation.

If an ambient temperature sensor concern is indicated the condition should be verified by performing the following test.
1. Measure the resistance at the ambient temperature sensor, (located at the center front of the engine compartment), at pins 8 and 13 of the electrical harness hardshell which plugs into the Automatic Temperature Control (ATC) head.
2. The resistance should be between 10,000 Ohms at 122° F and 125,000 Ohms at 23° F.
a. If the resistance at the sensor is incorrect, replace the sensor.
b. If the resistance between pins 8 and 13 at the ATC control head harness is incorrect check the wiring harness for an open or a short circuit condition.