When driving a Mercedes-Benz, you expect not only performance but comfort—especially when it comes to climate control. But if you’re experiencing poor cabin airflow, strange clicking noises behind the dash, or a persistent musty smell in the cabin, there’s a good chance you’re dealing with fault code 905807.
This code refers to a malfunction in the actuator motor that controls the air recirculation flap, and it usually points to a mechanical fault in the system. As a professional Mercedes-Benz electrician technician, I’ve encountered this issue in various models including the C-Class (W205), E-Class (W213), and even SUV models like the GLC and GLE. Let’s break down what this code means, how to diagnose it, and how to fix it properly.
What Is the 905807 Fault Code?
Fault Code 905807: “The actuator motor for the air recirculation flap has a malfunction. There is a mechanical fault.”
In simpler terms, this error indicates that the motor responsible for opening and closing the air recirculation flap is not functioning correctly—most likely due to a mechanical blockage, stripped gear, or a broken flap mechanism.
The air recirculation flap is part of the HVAC system and controls whether outside air enters the cabin or whether interior air is recirculated. It plays a key role in:
- Reducing dust or polluted air from entering the cabin
- Cooling or heating the cabin faster
- Maintaining proper humidity and comfort
How the Air Recirculation Flap System Works
When you press the “Recirculation” button on your AC control panel, an electric actuator motor turns to open or close the flap that separates outside air from inside air. This motor receives commands from the climate control unit (AAC/ACM) and feeds back its position using built-in sensors or potentiometers.
If the flap gets stuck or the motor gears break, the system can’t operate as expected. That’s when fault 905807 gets triggered and is logged in the climate control module.
Symptoms of a Faulty Air Recirculation Actuator
Here’s what I typically observe when this fault is active:
- Clicking or knocking noises from behind the dashboard (especially near the glove box area)
- AC not cooling effectively
- Cabin fogs up easily
- Unusual airflow behavior, like air not redirecting properly
- Foul or stagnant odor in the cabin (due to lack of fresh air circulation)
On most modern Benz models, the actuator motor will attempt to move the flap several times. If resistance is detected (due to blockage or broken gears), the system deactivates the motor and logs fault 905807.
Common Causes of Fault 905807
1. Stripped or Broken Plastic Gears
Over time, the small gears inside the actuator motor housing wear out. This is one of the most frequent mechanical failures I see in this system.
2. Blocked or Jammed Air Flap
Dust buildup, fallen debris (like leaves or insulation), or a swollen foam flap lining can physically prevent the flap from moving.
3. Loose or Disconnected Linkage
If the actuator motor becomes misaligned or the connecting arm to the flap is detached, the system can’t control the flap correctly.
4. Water Intrusion or Humidity
Vehicles exposed to leaks around the windshield or AC drain may suffer from corroded actuator internals or swollen flap materials, leading to jamming.
Diagnosing the Fault Properly
In my workshop, here’s how I tackle 905807:
- Use or compatible diagnostic tool to read fault memory from the AAC (Automatic Air Conditioning) control module.
- Run actuator tests via This forces the actuator to move and reveals whether the flap is stuck or motor is unresponsive.
- Remove glove box or lower dashboard panels to visually inspect actuator operation.
- Manually test flap resistance to determine if it moves freely or is jammed.
- Inspect the gears inside the actuator if noise or grinding is heard.
Repair Options
1. Replace the Actuator Motor
In most cases, the actuator motor assembly must be replaced. It’s often located behind the dashboard on the passenger side, near the HVAC
Important: Always ensure the new motor is initialized using diagnostic software. Some Benz models require the HVAC system to “learn” flap end positions after replacement.
2. Repair or Clean the Air Flap
If a blockage is the cause, cleaning or gently realigning the flap mechanism can resolve the issue. In rare cases, the flap itself must be replaced, which may require full removal of the HVAC airbox—a time-consuming task.
3. Software Reset and Re-Initialization
After mechanical repair, you must:
- Clear the fault code from the AAC control unit
- Perform an actuator adaptation or initialization process using Xentry or an advanced diagnostic tool
Prevention Tips
- Change cabin filters regularly to prevent dust buildup on internal HVAC components.
- Avoid running AC with windows down, which introduces contaminants and moisture.
- Check for signs of water leaks under the dash
Why This Repair Needs a Benz Specialist
While this might seem like a simple HVAC problem, it’s connected to a network of sensors, motors, and control modules. Improper handling—like forcing the actuator or skipping adaptation—can lead to new electrical faults or permanent damage to the HVAC system.
As a certified Mercedes-Benz electrician technician, I bring years of brand-specific experience and use factory-level diagnostic equipment like , allowing me to:
- Accurately diagnose mechanical vs electrical actuator issues
- Perform safe actuator replacements and recalibration
- Avoid unnecessary dashboard dismantling
- Ensure long-term performance of your HVAC system
Having Airflow Issues in Your Mercedes-Benz? Let Me Fix It the Right Way.
If your Mercedes is giving you HVAC errors like fault 905807, strange clicking behind the dash, or poor airflow control, it’s time to call a specialist.
I offer professional diagnostics and repair for all Mercedes-Benz HVAC and electrical systems, including:
- Air recirculation actuator motor replacement
- Flap mechanism repair and cleaning
- Climate control module diagnostics
- Electrical testing and system recalibration
Reach out today and get your comfort back—quiet operation, clean air, and perfect airflow, just like your Benz was designed to deliver. Mercedes Benz engineer Abuja 09015329867
