Theory Of Operation

The Mode and Temperature (Blend) Doors are opened and closed with electric actuators that provide a position signal. The LIN Signal is used by the HVAC module to monitor the door position. If the desired positions cannot be reached during normal operation, a DTC will set. All of the circuits are also monitored, either directly or indirectly, for open/short circuit faults. All 14 of the LIN powered actuators in the HVAC system receive a 12 volt power supply at Terminal 4 and receive a ground at Terminal 1. Terminals 2 and 3 are LIN Signals IN and OUT depending on the specific actuator. The last actuator in the system is a 3-wire actuator. Ground is at pin 1, 12 volts at pin 4 and LIN at pin 2. There are four circuits that run between each actuator and the HVAC Module:

• 12-Volt Driver Circuit 1
• LIN Signal (IN)
• LIN Signal (OUT)
• 12-Volt Driver Circuit 2

All communication between the 14 actuators is done from the front to the rear of the vehicle. If LIN communication is lost between #7 Rear Right Cold Blend Door and #8 Rear Right Hot Blend Door LIN communication between the remaining rearward actuators is lost and DTCs will set.