Automatic Temperature Control (ATC)

OPERATION
The ATC (Automatic Temperature Control) system communicates over the CCD bus (Chrysler Collision Detection mulitplex system) and for the first time allows diagnostics with the DRB III.

Through the CCD bus, the ATC Head receives engine temperature and engine RPM, to allow for cold engine blower lock-out and wide open throttle A/C cut-out. It also receives vehicle speed (for determination of the amount of air flowing through the condenser), a pulse width dimming signal, U.S./Metric status and the ambient air temperature. The ambient air temperature in previous years was hard wired to the ATC head. Bus communication allows the Body Computer to send the ambient temperature information to the ATC head and the overhead console.

The ATC head is responsible for maintaining the interior temperature of the vehicle based on the customer's input on the faceplate. The faceplate contains two large rotary knobs that control fan speed and mode selection. It also contains one small rotary knob for temperature control. One of the two buttons place the system in recirculation mode, the other defeats the A/C compressor unless the system is in the defrost mode. The ATC head samples outside air temperature, inside air temperature, vehicle speed, the amount of sunlight coming into the windshield and using an internal program, positions all the doors and blower speed to the appropriate settings. Because it is an Automatic Temperature Control system, it is able to adapt to different variations in outside conditions to allow for very accurate control of the inside settings. The temperature setting as selected by the customer appears in the display as well as the air direction.

The ATC head controls all of the actuators on the A/C housing. The actuators are electronic and all except the recirculation door actuator are equipped with a feedback strip. The actuators are electronic stepper motors that are positioned and tracked by the ATC head. The feedback strip allows the ATC head to keep track of the position of the individual motors. The blend door and mode door have several positions that are part of normal operation. The recirculation door is either open or closed and therefore doesn't need a feedback strip. The controller keeps track of the amount of time required to run the recirculation door through its entire travel and energizes it for more than this time to be sure it is at the proper location, either open or closed.

The icon on the control head is represented as a "stickman" and the arrow indicates the direction of the airflow inside the vehicle. There is also an outline of the vehicle with another arrow that represents the direction of airflow from the outside of the vehicle and whether the system is in recirculation mode. The A/C button allows the compressor to be switched off, except in defrost mode. A small snowflake symbol in the display indicates compressor operation. The recirculation button allows air to be drawn from the inside of the vehicle only, except in defrost. On high temperature/humidity days, recirc mode should provide better cooling than normal mode because the inside air is recirculated and re-cooled.

This system also allows increased flexibility because it can be operated in a manual mode. In manual mode the customer may select the airflow, fan speed, and whether the compressor will operate. The system can also be put into manual fan control by moving the fan control knob from automatic to one of the manual blower speed selections. Manual mode offers 10 different blower speeds, the automatic mode has an infinite number available.

OPERATION
The Automatic Temperature Control (ATC) system lets the operator change the passenger compartment comfort conditions. A computer, built into the control panel, regulates the desired temperature, air flow direction and blower speed. The operator may also select an AUTO mode feature in which the computer would select the blower speed and air flow direction.