How Does a Blend Door Actuator Work?

In many situations, you might not know that the heat of your car has stopped working until a cold morning in the winter when you adjust the temperature control of heater to the maximum setting.

It could be daunting if you think of attempting to troubleshoot the set of duct-work, hoses, and wires under the dashboard to solve the problem. A rather common issue in cars a couple years old, the air and heat system in your car might be the result of a defective blend door actuator.

Auto Heat​

A built-in heating system has been the standard equipment on many automobile models since the 50s and 60s. Back to the early stage of motoring, the heater was an optional device and most possibly protruded rather clearly from the bottom of your dash.

One factor that has been consistent over the past few years is that the source of heat for a car heater will come from the coolant of the engine in most car models. This coolant is sent from an engine although the heater core, which has the same look with a small radiator, built in the heater assembly within the passenger cabin.

A blower engine will force hot air to the passenger cabin from the core. These days, heat’s temperature in modern cars is often controlled by a blend door regulated by an actuator, which might also change the direction of all or some of the heat to a windshield defroster.

Recommended for You: 

Air Conditioning​

Early air conditioners on car were just the add-on equipment, which were possibly no installed at the factory, but by the dealership. These types of air conditioner were completely independent of the heater and were built noticeably under the dash like an early heater.


As of 2013, the air conditioning and heating systems in many automobiles share a lot of elements such as the duct-work under the dash, the control of temperature on the dash’s face. With the combination of both systems, the blend door actuator controls the conditioned air’s temperature and leads it to the needed location.

​Blend Door

In general, the blend door is built within the pivots and air as well as heating conditioning system to divert cool or warm air to different directions inside the system to keep the temperature in passenger compartment at the needed amount.

When a car is cold, the driver might want to maximize the heat to come in a passenger area. In this situation, the car may move the blend door to divert most of the heated air to the cabin.

After warming up the vehicle, the blend door will be shifted to change just a part of the heated air to the cabin. When the air is cool enough, the door will be closed so that no heat would enter the passenger compartment. Blend door moves by a mechanical unit known as the actuator.

Blend Door Actuator​

In some car models manufactured before 1980, the blend door might have been activated by metal cables, which were directly connected to the lever of temperature control on the dash. A certain method to move a blend door, a couple of systems would take more than a little time and effort to control.

Since automobiles have been made with more and more labor-saving units as the standard, air and heat conditioning controls would be controlled with less effort when manufacturers started setting up blend door actuator, which automatically helps to move a blend door when the system moves temperature control.

An actuator could be powered by a small engine built in the air and heat assembly or vacuum.

Actuator Failure​

Like any other mechanical units, a blend door actuator would eventually fail. Replacement elements to fix the issue might cost you a few USD, but the expenses of labor for replacing it might be up to hundreds. It is due to the fact that the actuator is placed within the air and heat assembly under the dash.

When some cars are manufactured in the factory, the whole dash, including the air and heater assembly, might be placed together as the whole unit before the installation to the vehicle. To change an element in this complicated system, you need to remove many other elements first. While this might be a difficult task, it could be achieved by a good mechanic specialized in regular automotive device.


Does Octane Booster Work for Your Vehicle?

A Comprehensive Guide to Limp Mode in Car


5 thoughts on “How Does a Blend Door Actuator Work?”

  1. I have an H2 hummer SUT. My havoc system, only blows air throw the upper defrost vents. It will not transfer to anything lower. However also another issue, is it blows cold on the drivers side and hot on the passenger side, during these months. Vice virus during the cold months.

  2. My 2013 Nissan Altima A/C only blows at 60 degrees and no colder. I changed 3 compressor the condenser. Checked the high and low pressure lines. And still 60 degrees


Leave a Comment

Your Auto Space