Heating and Air Conditioning: Description and Operation

Fig. 9 Electronic automatic temperature control system block diagram.:

The electronic automatic temperature control system uses a micro-computer to analyze five major inputs,

1. Temperature, mode, and blower selections (made by the driver or front seat passenger).
2. In-vehicle temperature.
3. Ambient temperature.
4. Engine temperature.
5. Sunload sensor.

Then uses this information to determine the correct conditions of six outputs,
1. A/C compressor clutch engagement
2. Blower speed.
3. Blend door position.
4. Floor-panel door position.
5. Panel-defrost door position.
6. Outside-recirc door position.






A small DC electric motor or actuator is used to operate the temperature blend door. Vacuum actuators are used to control each of the three remaining air distribution doors. A feedback circuit is used in the blend door actuator to supply the control head with blend door position information. The blower motor 18 controlled by the control assembly through the blower speed controller and the high-blower relay. The blower speed controller and the high-blower relay are required to convert a low power signal from the control heed to the high power signal required to drive the blower.shows the control assembly response to the function knob selections.

A Self-Teat feature has been included in the control assembly to supply the technician with error codes.These codes direct the technician to the damaged component.