HVAC System

Schematic:

CIRCUIT DESCRIPTION
The solar/twilight sensor is a photo-electric cell that provides two inputs to the heater and A/C control system. The input for the sunload is at terminal 3 of the heater and A/C control. This is used by the controller for temperature control compensation based on additional heat from the sun (sunload.) The input for the twilight sentinel is at terminal 2. The twilight sentinel input is then processed by the controller and sent to the Body Control Module (BCM).

CONDITIONS FOR SETTING THE DTC
The heater and A/C control continuously monitors CKT X812. The circuit needs to stay at or near zero volts for 200 ms.

ACTION TAKEN WHEN THE DTC SETS
^ Stores a DTC 38 in the heater and A/C control memory.
^ The system will default to a assumed value of no solar heat (darkness).

CONDITIONS FOR CLEARING THE DTC
^ The conditions for the fault are no longer present.
^ Using a scan tool.
^ A history DTC will clear after 20 consecutive ignition cycles if the condition for the fault is no longer present.

DIAGNOSTIC AIDS
^ If the DTC is a history or intermittent. Try performing the tests shown while moving the wiring harnesses and connectors, this can often cause the malfunction to appear.
^ Visually inspect sensor connector and harness for damage, corrosion or water intrusion.
^ Check for adequate terminal tension, mis-routed harness, rubbed through wire insulation, and broken wire(s) inside the insulation.

TEST DESCRIPTION

Steps 1-8:

The number(s) below refer to the step number(s) on the diagnostic table.
2. This step tests the reference voltage from the heater and A/C control.