Heating and Air Conditioning: Description and Operation

Fig. 1 Comtrol Assembly:

The EATC system consists of an electronic control amplifier, Fig. 1, three servo motors, three blower motor relays, a transistor and the blower motor. The system controls blower speed, recirculated/fresh air mix, air temperature and air venting to the passenger compartment. The blower has an adjustable range controlled by the 1/2 turn speed switch. The blower fan speed is controlled by a linear power transistor. This eliminates the need of a blower motor resistor assembly.
The servo motors used to control airflow are mounted directly to the blower unit and heating unit, and are removable from their mechanical linkage. The blower relays are mounted on the heater unit with the blower motor. The transistor is mounted in the fan airstream to allow cooling during operation.