Mercedes-Benz ML55 AMG HVAC Blend Door Actuator Replacement Cost

To blow heat into the cabin, the blower motor sends air through the heater core and on through the dash vents. But when heat is not desired, the blend door actuators direct that airflow away from the heater core. There are also actuators to direct air to the dash vents, floor vents and windshield vents depending which setting is selected.

In addition to improper temperature and/or air flow output from the dash vents, you may also hear a clicking noise from behind the dashboard.

The symptoms of a bad blend door actuator include a lack of heat or air conditioning, or failure of air to blow through some or all of the vents. The actuator motors may also make a noise if they've failed, but this isn't always the case.

Driving with a bad blend door actuator may not be comfortable, but it won't hurt the vehicle. 

Blend door actuators fail frequently on some vehicles, but not in others. So, the rate of failure will depend on the vehicle make, model and year.

The technician will test each vent position and temperature range. The amount of air and its temperature will be noted for each setting. If there's no change between settings, the blend doors are a strong possibility. When these components are suspected, testing the circuit and observing them while they're working are the only ways to test them. The electrical wires or vacuum lines will be inspected to ensure the proper amount of power is being delivered. From there, the parts can be bench tested to pin down the problem.

Replacement procedures vary by vehicle. Some actuators will be easy to access, but others will require removing the airbags and dismantling the dashboard or parts of it. Most modern vehicles, especially those with dual climate control features and rear passenger air options, can have several blend doors and actuators. 

Depending on the vehicle the replacement of the Blend Door Actuator will require the removal of the dashboard. This adds considerable labor costs, increasing the overall price of this repair.

We don't recommend using DIY universal blend door correction kits, as these kits involve cutting into the HVAC ducts and replacing OEM components with generic components.