Low Airflow From Vents

The air vent system in your car is designed to direct airflow through various ducts. These ducts perform operations from defrosting the windshield, heating your feet on a cold day or cooling your face during a hot summer day. If the air delivery system has failed or has low airflow there is a problem. We have listed the most common causes below:

Step 1 - Plugged Air Cabin Filter - Most cars today are equipped with a cabin air filter or hepa filter. These filter are designed to filter the air before it exits the air ducting. If this filter becomes clogged due to lack maintenance it will stop or slow the flow of air exiting the vents. To check this filter you must locate the filter housing. These filter housings can be either under the dash on the passenger side or under the hood of the car, near the base of the windshield. Next remove the cabin air filter and inspect and replace if needed. To see how an air cabin filter is changed by watching the video below.

Step 2 - Check Air Control Adjuster - Most air control vents are equipped with a flow control door that is located at the vent outlet. This door is controlled by a thumb wheel that when activated will open and close the vent air flow door. To check the vent air flow door control, apply the emergency brake and put the car in park. (If quipped with an automatic transmission). Start the engine and allow to idle, next set the heater or air conditioner to the highest airflow setting. Work the thumb wheel from one side to the other while checking the airflow. The flow should stop and start again, if the thumb wheel does not make a difference the problem is somewhere else.

Step 3 - Testing Blower Motor - All cars utilize a fan blower motor. This motor is control by either a switch in the user compartment or a computer depending on the system the car is equipped with. If this fan motor is starting to short out (one pole of the armature out of three has shorted) it will cause the fan motor to run at 2/3 speed and not move as much air as a fan motor that is operating correctly. To test this condition you will need an amp meter, connect the meter lead to the power wire of the fan motor. With the fan motor on in the full speed setting the amp meter should read between 9 and 15 amps. Anything lower than 9 amps could mean the fan motor has shorted and is not operating at full output.

Step 4 - Checking For Vent Inlet Restriction - What comes out of your air vents must go in. The air intake for the vent system has two air intakes. One air intake is meant to be used when the system is set to the fresh air setting. When the system is in the fresh air setting it will bring air from the outside of the car to the inside. When the system is set to the recirculation position air is circulated from the inside of the car. If these air intakes become plugged by a piece of paper cloth or other form of blockage it will slow or stop the airflow from the intake of the system. Inspect both external and internal air intakes. These intakes are located at the base of the windshield (external) and at the passages side foot well (internal).

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Written by
Co-Founder and CEO of
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-08-16)