System Description

CLIMATE CONTROL SYSTEMS
Automatic Temperature Control (ATC)
The body control module (BCM) provides for automatic temperature control support both through PCI bus communications and through processing inputs to determine control for actuators and the blower motor. The BCM interfaces with the ATC control head over the PCI bus. Information on button activation, blower setting, and temperature setting are supplied to the BCM. In turn, the BCM supplies the ATC control head with mode information and indication lamp status. The BCM controls blower motor speed by providing a varying duty cycle of a fixed frequency output (pulse width modulation). There are 14 distinct blower speeds, plus a blower OFF signal. The body control module also controls the HVAC mode, temperature (blend air), and recirculation doors. This system is either fully automatic or fully manual control (no semiautomatic functions); however, the temperature blend door control is always automatically controlled based on sensor reading and comfort setting. The in-car sensor and the aspirator motor are 5/10/99 housed in the ATC control head.

Manual Temperature Control
The body control module interfaces with the A/C heater control head via hardwired circuits. Information for the temperature setting is supplied to the body control module via a potentiometer. The rear defogger switch, A/C switch and the mode setting is supplied via a resistive multiplexed circuit. The system ON/OFF status is supplied by a dedicated circuit. The BCM drives the A/C and rear defogger indicator lamps via hardwire to the A/C heater control head.