Automatic Zone Control

AUTOMATIC ZONE CONTROL (AZC)
The AZC (Automatic Zone Control) system will be the auto industry's first sport utility vehicle to offer automatic dual-zone temperature control with infrared sensing technology for superior occupant comfort. With AZC, occupants select a comfort temperature, not the actual passenger compartment air temperature. The temperature in the passenger compartment at any time may be slightly higher or lower than the selected value. For instance, on sunny summer days the air flow will probably be cooler than the comfort temperature; on cold or cloudy days and at night it will probably be slightly warmer.

A simplified control system for operation of mode, recirculation, and temperature control doors provides positive positioning without the complexity of feedback from position sensors. Knowing the number of operating motor revolutions required to provide fuel travel, and the number of motor commutator pulses per revolution, the control system runs the motor for the number of commutator pulses corresponding to the desired door position. To maintain accuracy, the system recalibrates itself periodically at known zero or full travel conditions.

The AZC blower control provides continuously variable control of air flow rate to meet occupant comfort requirements. Pulse-width modulation of blower power allows the blower to operate at any speed from stationary to full speed.

The AZC module uses infrared sensing technology to control occupant comfort levels, not the actual passenger compartment air temperature. Dual infrared sensors mounted in the face of the control unit independently measure the surface temperature to maintain customer-perceived comfort temperature under changing conditions. Dual zone temperature control provides wide side-to-side variation in comfort temperature to exceed the needs of either front seat occupant. This sensing system replaces interior air temperature and solar sensors used to approximate direct sensing control through complex control programs.

The infrared temperature sensor cannot be adjusted or repaired and, if faulty or damaged, the module must be replaced.

NOTE: THE INFRARED SENSOR WINDOW MAY BE PERMANENTLY DAMAGED IF ANY TYPE OF COSMETIC VINYL DRESSINGS ARE ALLOWED TO CONTACT THE LENS. AVOID SPRAYING OR WIPING THIS AREA WITH ANY CLEANER OR CONDITIONER. THIS MAY RESULT IN IMPAIRED TEMPERATURE SENSING AND CONTROL.

FUNCTIONAL OPERATION
The AZC system communicates over the PCI bus (Programmable Communication Interface multiplex system) and allows diagnostics with the DRB III.

Through the PCI bus, the AZC 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 for the VF display. U.S./Metric status, and the ambient air temperature. The ambient air temperature in previous years was hard wired to the ATC head. Now bus communication allows the Body Control Module to send the ambient temperature information to the AZC head and the overhead console.

The AZC head is responsible for maintaining the interior temperature of the vehicle based on the customer's input on the faceplate and the I/R sensor input. The faceplate contains two large rotary knobs that control fan speed and mode selection. It also contains two smaller rotary knobs for the temperature control of each zone. One of the three buttons place the system in recirculation mode, the button across from that, turns the A/C ON or OFF. The third button on the bottom, turns the Rear Defogger ON and OFF. All three of these buttons contain a LED indicator showing an ON or OFF state. The figure in the VF display on the control head is represented as a "stickman", and the arrow indicates the direction of the airflow inside the vehicle. The A/C button allows the compressor to be switched ON or OFF, except in defrost and automode. The Recirc 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 within the vehicle.

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.

The AZC system in 2001 is fully addressable with the DRB III and it still retains the on-board diagnostics from the past years. For more thorough explanation of the on-board diagnostics, please refer to the Service Information. All of the inputs to the AZC head can be read with the DRB III and some outputs can be actuated. Diagnosis of the AZC system should begin with the reading active codes on the DRB III. If no active codes are displayed, read the stored codes next.

If any of the motor actuators are replaced or the A/C, heater housing is replaced, the system should be recalibrated. This happens automatically at battery disconnect or it can be accomplished using the DRB III. Without recalibration, the AZC head will not be sure of the actuators position and may reset in poor air control.

Active Codes
An active trouble code indicates an on-going malfunction. The defect is present every time the AZC head checks the circuit or function. It is not possible to erase an active code. Active codes will change to stored once the reason for the code has been corrected.

Stored Codes
A stored code indicates that there was an active code present at some time. The reason for the active code was corrected and the code was changed to the stored code.

If the reason for the code was corrected, the AZC head will erase the code after 72 keys cycles. The code may also be erased from the head using the DRB III.

If no obvious problems are found, read active codes on the DRB III while wiggling the harness and connectors. Recheck for codes periodically as you work through the system. This procedure may uncover a malfunction that is difficult to locate.