Symptoms Of A Bad Blend Door Actuator

Automotive transmission parts

The blend door actuator is a small electric motor that is an HVAC system component and controls the car’s temperature and airflow. The interior has a few plastic gears and it looks like a small plastic box. The blend door actuator works together with the sensors connected to the car’s climate control system to control the defroster and vents.

When turning the dial to adjust the temperature, the signals pass through the blend door actuator to regular the airflow to the desired temperature. It thus helps in deciding whether the air passes through the floor vents, mid vent, or control defrost. By knowing the symptoms of a bad blend door actuator, you can quickly repair the blend door actuator and prevent future discomfort to you and your passengers. Here are some of the signs of a bad blend door actuator.

Knocking Sounds

Whenever you hear a knocking sound when starting the vehicle or turning on the HVAC system, the main culprit is usually the blend door actuator. This is because knocking sounds are usually attributed to a failing blend door actuator and are one of the signs that you should replace your actuator.

Inconsistent Temperature

If the temperature coming out of your car’s air vents is inconsistent, it may be an indication of a bad blend door actuator as an oscillatory moment of the blend door will cause incorrect diversion of the airflow, resulting in inconsistent temperatures.

Inconsistent Airflow

If the airflow coming out of your car’s air vents is also inconsistent, it may also signal a problem with the blend door actuator. This is because a bad blend door actuator will result in the blend door constantly moving back and forth, which again results in the airflow being wrongly diverted.

Wrong Temperature

Bad blend door actuators are the primary cause of a faulty climate control system. If your car’s air conditioner constantly blows hot air instead of cool air or does not heat up to the proper operating temperature, then you should have the blend door actuator inspected by a mechanic. A blend door actuator may be damaged due to the plastic gears being worn out or the actuator failing. This will result in the vehicle’s climate control system not functioning properly.


Pay close attention to the dashboard when turning on the air conditioning or climate control system in the car. If you constantly notice a repetitive faint clicking or droning sound from the dashboard in the center area, then it is a sign of a bad blend door actuator, as this is where the HVAC system control knobs are located.  

Sometimes switching the climate control dial may stop the noise temporarily. However, if the bad blend door actuator is left untreated and continues to deteriorate, the plastic gears will break off and cause slipping when you turn the HVAC knobs. To prevent this, it is best to book an appointment with a professional and have your car serviced properly with a mechanic as soon as possible.