Electronic Climate Control

Fig. 1 EATC Control System:

The electronic automatic temperature control system uses a micro-computer to analyze six major inputs, then uses this information to determine the correct conditions of six outputs (illustration).
The micro-computer analyzes input from the A/C pressure switch, manually selected temperature and mode, in-vehicle temperature, ambient temperature, engine temperature and sunload sensor. This information is used to determine the correct conditions of A/C compressor clutch engagement, blower speed, blend door position, floor-panel position, panel-defrost position and outside-recirc door position.
A small DC electric motor or actuator is used to control the temperature blend door, while vacuum actuators are used to operate each of the three other air distribution doors. The blend door actuator uses a feedback circuit to supply door position information to the control head. The control assembly controls the blower motor through the blower speed controller (BSC) and high-blower relay. The controller and relay convert a low power signal from the control head to a high power signal required to drive the blower.
A self test feature is incorporated into the control assembly which provides error codes to determine the damaged component(s).