The air delivery is controlled by electronic actuators
mounted on the HVAC module. The actuators are electronic stepper motors equipped
with feedback potentiometers. The heater and A/C programmer (heater and A/C
programmer) determines the position of the actuator shaft based on the voltage
from the potentiometer. The heater and A/C programmer controls the actuators
with only three different voltage signals:
| • | 0 volts drives the actuator to its minimum position. |
| • | 5 volts drives the actuator to its maximum position. |
| • | 2.5 volts stops motor rotation. |
The heater and A/C programmer uses inputs from the temperature sensors,
heater and A/C control, steering wheel controls and passenger temperature
control to determine how the actuators should be positioned.
Four actuators exist: air inlet, mode, left air mix and right air mix:
| • | The air inlet actuator controls the outside/recirc door position.
There are only two positions of operation for the air inlet actuator. The
heater and A/C programmer commands the air inlet actuator to provide either
outside or recirculated air to the inlet of the HVAC module. |
| • | The left and right air mix actuators control the amount of air
that flows around or through the heater core. The heater and A/C programmer
can command the air mix actuators to any door position from full heat to full
by-pass. |
| • | The air discharge is controlled by the mode door actuator. The
actuator drives a cam wheel that controls the position or the two air discharge
doors. The heater and A/C programmer commands the mode door actuator to any
one of 5 positions. |
