HVAC Programmer

System Block Diagram:

The HVAC programmer is the "brain" of the dual air conditioning system. The programmer receives electrical signals from the heater and A/C control assembly, passenger climate control assembly, RH solar sensor, LH solar sensor, ambient temperature sensor, in-vehicle temperature sensor, blower control module, Powertrain Control Module (PCM), driver air mix valve actuator and passenger air mix valve actuator. A microprocessor in the programmer processes these signals and then sends commands to the system components that control A/C compressor operation, air discharge location, air discharge temperatures (driver and passenger sides) and blower speed.

The solenoid-actuated vacuum valves, which control air discharge location, are located inside the HVAC programmer. There are four valves; each controls vacuum to a separate vacuum diaphragm. By energizing various combinations of these solenoid-actuated vacuum valves, the HVAC programmer can control whether air comes out the floor outlets, panel outlets, or windshield outlets and whether fresh (outside) air is drawn into the system or inside air is recirculated.

The HVAC programmer microprocessor also performs self-diagnostic functions for the system. The microprocessor identifies faults in the temperature sensor, solar sensor and air mix valve actuator circuits when the system is operating and stores this information in memory. Then, when the system diagnostic mode is activated, these faults are displayed as numeric diagnostic trouble codes on a Tech 1.