Why Air Only Blows Through Defrost Vents?

You are driving a car when the only way to get air is through the defrost vents, and other vents aren’t functioning. Don’t worry the article discusses air only blows through defrost vents. Read until the end to find out the solution. Hope you will enjoy reading the article.

Why Air Only Blows Through Defrost Vents?

The air surrounding the car will be sucked into a duct in the front and a few small ones along the grill located above the bonnet when the car moves at high speeds due to high pressure While entering the vehicle, it will be warmed or cooled by the air conditioner as the airflows outside, then spread out the place through air ducts scattered inside the cabin. Lastly, these airwaves will then pass through the air vent at the rear to exit thus ending a smooth ventilation cycle within the car cabin.

These days, in some vehicles there is a different ventilation system installed, where the air recirculates inside the vehicle’s cabin without being blown out. While warming or cooling them these air out iissucked again and, then blow it back into the car. If you do not want any hot, humid, or smelly air creeping into your car while keeping the air inside the cabin fresh and cool then this system set in this form will be beneficial.

Why Does Air blow Through Defrost Vents?

1. Damaged Blower Motor

The job of the blower motor is to push the air through the vents. Combined with the blower resistor, it will also control how much air is blown.

A damaged blower motor prevents air from going through your vents, resulting in no airflow at all.

Hear the vibrations or high-pitched noises when your blower motor becomes damaged. You’re most likely to smell your blower motor burning because of overheating.

Your blower will become damaged if the internal motor components have been rusted and overheated due to airflow restrictions and bad bearings.

2. Bad Mode Door Actuator

The first cause of AC only blowing through defrost vents is a faulty door. The mode door actuator functions to control the vents according to the custom setings to ensure that air will be blown out properly.

Nowadays, many modern door actuator systems have been gradually developed based on automation. As you can notice, even modern systems that integrate multiple types of high-performance technologies will wear and break down over time, let alone the manual ones. The actuator is always in a vulnerable stage as it is often exposed to air from different raw air sources

3. Clogged Air Intake

Two spots in your car from where air can enter:

  • The vents on the lower half of the shield
  • The duct from where the air is being recirculated

When both the locations are obstructed by dirt or a clogged air filter then only the air will be blown through defrost vents.

Lack of steady flow of air affects the air temperature and debris such as tree nuts, fall leaves, sticks, or bird nesting materials can cause clogging.

Clogged intakes will make it impossible to clear windows quickly, as there is no airflow. Due to clogged air intake, there is foul air in the car.

4. Faulty Blower Resistor

The blower resistor will blow cool or warm air through the vents when you turn on the air conditioner/heater and adjust the car air fan to operate at multiple speeds to suit your needs. Your wind resistor may be faulty and needs intermediate repair when the car AC is stuck on defrost vents.

Overheating or thermal overload is the leading cause of this problem. So, to give the blower resistor total control of airflow rate and strengthen the cabin air, it has to be replaced at a professional repair shop by a professional only.

5. Electrical Issues – Bad Relay

A relay regulates the current needed for ventilation. The relay must provide the current for the blower motor to be operated properly.

If this doesn’t occur, the ventilation is restricted, forcing air to blow through the defrost vents.

I’d to the stress of constantly switching on and off the relay wears out very fast. You can notice this when the relay has become faulty by the blower and not responding.

The relay could not handle the current and this is indicated by a blown fuse. Another indicator of a bad relay is when it feels warm to the touch, this means that the relay retained excess heat due to malfunctioning.

How To Fix AC Stuck On Defrost?

Step 1: Take Care Of Your Damaged Blower Motor

The only way to care for a damaged motor is by identifying what the cause is and addressing the issue. Take care of the ducts if it is overheating due to air restriction.

Rust means dirt is getting to your blower motor. Check and fix any leakages in the furnace and replace air filters.

Step 2: Fix The Blend Door Actuator

Perform a blend door repair to temporarily get some heat once you identify that the blend door actuator is not working.

If it’s damaged then replace the blend door actuator. You can go to an expert if you have no confidence in matters of motor repair.

Step 3: Unclog The Air Intake

Cleaning and possibly replacing the air filters will go a long way in unclogging the air intake.

It would help if you had your air intake clean for contaminants to be filtered and to avoid problems for you and your passengers. Homemade solutions are also very helpful to clean your air intake, which will prevent air from blowing through defrost vents only.

But you can also find cleaning solutions in the supermarkets. Try to make sure you clean at least weekly.


The above article discussed air only blows through defrost vents. Hope the information was useful. If you have any query with the mentioned information then please leave a comment below we will get back to you as soon as possible.


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