Blend Door Actuators

The blend door actuator or the blend door is a part of a vehicle that helps combine the hot air with the cold air. The actuator is a motor that opens and closes this door to adjust the amount of hot or cold air to achieve ideal temperature setting. If your blend door actuator breaks then you may only have hot air or cold air exclusively, and no air conditioning.

What the Actuator Does
Inside the blend door actuator, you will see round shaped gears, a motor, and a circuit board. The round shaped gear blends rotate the actuator that opens and closes the vent to allow the air to pass through. These round shaped gears have teeth which most often than not breaks and it causes the actuator to not function as should be. In other words, the gap from broken teeth prevents the gears from rotating the actuator shaft.

Blend Door Actuator in Older Cars

In old model cars, blend door actuators are being controlled by a lever located at the AC panel. It is then connected to a wire that goes to the blend door. It was later on replaced with a computer that controls the blend door with the use of a pseudo stepper motor to control the door. The end point detection is the door movement and for computer algorithm to control the door and the system needs to know when if the door is closed against the heater core or if it is blocking the free air flow through the vent.

In order to do this, the motor and the door must be driven to a stall point to detect the voltage surge that comes from the motor as an indication of the extent movement. And because this is not helpful at all, professional mechanics today stopped using this system because plastic doors do not have resistance to calibration routine and if over stressed, it will break. If this happens, heat and AC control will be lost.

Blend Door Actuator in Modern Cars
In most cars today, the air is usually blown through the AC evaporator core. The blend door actuator will then redirect the air through the heater core. When you are on full AC mode the blend will close against the heater core, in that process all the air will flow around the heater core and into the vent system.

If you are in heater mode, the compressor is shut off and so there will be no changes in the temperature. The air will then be flowing into the AC evaporator core and then will be directed to the heater, and finally into the vent system.

Common Blend Door Problems and Solutions
1. The vent system blows hot air
The cause may be the blend door actuator’s gear teeth is broken and so the actuator must be replaced.

2. No heater
It can either be because of a broken blend door or a defective actuator. You should try recalibration to know the real cause of the problem.

3. Fan is working but no heat is coming out
In this case, the tip of the crack of your blend door may be broken that is why it is not letting the actuator motor close the door to heat up the air.

4. The fan is only working at one speed
It means that the motor resistor is not in a good condition and need replacement.

5. The fan is only working in one direction
This might mean that the vacuum solenoids or the blend door motors is not working well, you can simply check if there is power on the vacuum, if there is then you might want to check the control unit located at the dash.

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