Blend door actuator: how it works, when to replace?

January 15, 2022
In the car's heating ventilation and air conditioning (HVAC) system, there are several air doors that direct the flow of air through the system.
Blend door actuator Blend door actuator.
In many cars these doors are operated by electrical actuators. For example, the actuator in the photo controls the Fresh Air/Recirculation mode door. The electric actuators are typically called door actuators or blend door actuators. Problems with blend door actuators are common in many cars. Read also: Car heating system: how it works

Blend door actuators problems: One of the common problems with blend door actuators is when the gears inside wear out and start skipping. The typical symptom of this problem is a repeated clicking noise coming from under the dash. Often the noise lasts for a few seconds when changing the HVAC modes or turning on the heat or A/C. Another common problem is when one of the blend door actuators works intermittently or stops working completely.
Problems with a blend door lock actuator cause variety of issues with heating and air conditioning. For example, the air could be not warm enough when set to heat or not cold enough when set to A/C.
Blend door actuator visible from the glove box opening Blend door actuator visible from the glove box opening.
Another common issue is when the dual heating or air conditioner works good on one side of the car, but doesn't work properly on the other side.

Because HVAC issues can be caused by many other problems and testing blend door actuators is difficult, we suggest to get the diagnostics done at your dealership or a local shop that has an advanced scan tool. In some cars, a failed blend door actuator may set the trouble code. Using the scan tool, the mechanic can read the code and test the actuators.
If a faulty blend door actuator is confirmed, it will need to be replaced. The part is not expensive, however, due to the location, the labor charge could be quite high.

Blend door actuators replacement: The main difficulty with replacing one of the blend door actuators is their location under the dash. In some cars, the actuators can be accessed through the glove box or from the driver's side. In some trucks the actuators are placed at the bottom of the HVAC unit. In some cases a dashboard might even need to be removed to get access, although there could be ways around it. If you prefer a DIY repair, Youtube has many videos on blend door actuators symptoms and replacement.

Blend door actuator inside Blend door actuator inside.
How a blend door actuator works: Inside a typical blend door actuator there is a circuit board, a little electric motor, several reduction gears and the sensor that tracks the position of the blend door. If one of the gears wears out and start skipping, the blend door actuator might produce a repeated clicking noise when operated. If the position sensor wears out, the blend door actuator will not know the position of the blend door and might hunt for the right position, work intermittently or stop working completely. If the motor wears out, the actuator might stop working or produce a screeching noise when operated.