Air Door Actuators
Air conditioning cases contain air doors that control the flow of air through the system. There are at least three diverter doors and one blend door in the basic air conditioning system. Diverter or mode doors are typically either open or closed, while blend doors that mix air have many positions.
These air doors are controlled by cables and vacuum or electric stepper motors depending on the age and type of vehicle. Cables were used in older models to control mode and blend doors. These were replaced with vacuum motors and electric actuators.
Vacuum operated controls are great for doors that are either open or closed. The outside air recirculation door is an example of a door that is often vacuum controlled. An air blend door needs more precise control. This is why electric stepper motors are used. These actuators have many positions (0 – 255).
When closed, the blend door blocks air from passing through the heater core providing maximum cooling. As it opens, it allows more and more air to pass through the core; mixing the air provides the desired temperature.
Electric actuators often require replacement for failure or making a clicking sound in operation. This is because as they wear the end points change or the plastic gears inside the actuator have broken or stripped.
When replaced, they typically require calibration. The actuator motor contains a controller that receives a voltage signal from the main controller. It moves the blend door to a position that matches the signal to provide the desired temperature. Many contain potentiometers that provide door position feedback to the controller.
The method used to calibrate the actuator depends on the manufacturer. Some systems have a procedure that involves momentarily removing and then replacing the HVAC fuse and then waiting a specified period of time while the motors move from end to end and synchronize with the controller. Some require the technician to press and hold two buttons on the panel while the motors calibrate. The climate control mode of a scan tool is used to calibrate newer vehicles with automatic climate control systems.