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Why Does Air Only Blows Through Defrost Vents?

Imagine you’re driving your beloved car on a sunny day and you suddenly realize your air conditioner air only blows through defrost vents while the others stop working. It can be quite frustrating when it comes to dealing with those car problems and their repairs. However, it can get even more frustrating when you don’t know the reason behind what is wrong with your vehicle.

In the seasons like summer or winter, as we often turn on the air conditioner to keep warm or cool the body when traveling, the air vents may have to work continuously and lead to abuse. After a long time of continuous use, they may become clogged, smelly, or damaged.

In this article, we’ll look into the specific causes of such inconvenience. Let’s get started.

Reasons Behind Air Only Blows Through Defrost Vents?

There are various reasons for air only blowing through defrost vents.

1. Faulty Mode Door Actuator:-

The mode door actuator works to control the air that blows through the vents. Modern door actuators are electronically controlled, and they wear out over time. The mode contains plastic gears that can break or strip.

Application errors like excessive loading, incorrect wiring, or poor mounting can cause the actuators to malfunction. When there is a clicking sound, the mode door actuator is likely faulty. Eventually, air will only blow through defrost vents instead of all vents.

2. Damaged Blower Motor:-

The blower motor pushes 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.

Wear and tear can cause your blower motor to become damaged. You will hear vibrations or high-pitched noises when your blower motor becomes damaged.

3. Bad Relay- Electrical Issue:-

A relay regulates the current needed for ventilation. The relay wears out very fast due to the stress of constantly switching on and off. A blown fuse can indicate that the relay could not handle the current.

ac stuck on defrost

For the blower motor to operate, the relay must provide the current. If this doesn’t occur, the ventilation is restricted, leading to the issue of air only blows through defrost vents.

4. Faulty Blend Door Actuator:-

A blend door actuator controls the temperature by allowing or blocking the air that passes through the heater core. It has plastic gear which is fragile and can break easily. The blend door actuator can also stop working when the electric motor burns out.

If you get inconsistent temperature, your actuator is likely broken. You will also hear ticking from the dash before the blend actuator becomes fully damaged.

5. Blown Fuse In The Ventilation System:-

A fuse plays a vital role in the ventilation system and protects the components from electrical surges. Once the fuse is blown, your air conditioner will not work. A blown fuse means there is no more power to the blower motor. Air blowing through defrost vents only means the fuse for your ventilation is blown.

6. Faulty Blower Resistor:-

A blower resistor pushes air through the vents when using a heater or an air conditioner. It allows the air fan in the car to be operated at different speeds. When you add air pressure, and nothing happens, your blower resistor is damaged.

Air Only Blows Through Defrost Vents

Overheating is usually the leading cause of a failed blower resistor. If you cannot regulate the airflow rate, your blower resistor is damaged due to which air only blows through defrost vents.

7. Clogged Air Intake:-

The air only enters in the vents on the lower half of the shield and in the duct where the air is being recirculated The air will only blow through defrost vents when both locations are obstructed by dirt or a clogged air filter.

Clogged air intakes are mostly caused by obstacles falling into the air vents when you are traveling on the road, such as tree nuts, fallen leaves, long sharp sticks, or branches of bird nests. Clogged intakes will make it impossible to clear windows quickly, as there is no airflow.

How To Fix The Issue Of Your Air Only Blowing Through Defrost Vents?

If you’re facing the issue of air only blowing through defrost vents. Here are the solutions for it.

Step 1:- Unplug The Faulty Mode Door Actuator

The first thing to do with a faulty mode door actuator is to unplug it. Using your fingers, rotate the car’s mode door linkage shaft. Confirm whether it is moving freely, which means it’s working. Try and do some cleaning as this will unclog some of the greases.

Step 2:- Identify The Cause Of Damaged Blower Motor

The only way to care for a damaged motor is by identifying what caused it and addressing the issue. If it is overheating due to air restriction, then take care of the ducts. Rust means dirt is getting to your blower motor. Check and fix any leakages in the furnace and replace air filters.

Step 3:- Fix The Bad Relay

If you cannot replace the bad relay yourself, take it to the workshop or consult a professional. It is advisable to take your damaged relay to the automotive shop to get the right relay part.

Step 4:- Fix The Blend Door Actuator

Replace the damaged blend door actuator. If you have no confidence in matters of motor repair, you need to get an expert.

Step 5:- Repair Or Replace Your Damaged Blower Resistor

You cannot repair a damaged blower resistor. Once fixed, your air vent will function properly, and air will not only go through defrost vents.

Step 6:- Replace A Blown Fuse

It’s always advisable to replace a blown fuse before it causes further damage. But if it blows again after replacing the fuse, there is an underlying issue. Take your car to a professional mechanic.

Step 7:- Unclog The Air Intake

Cleaning and possibly replacing the air filters will go a long way in unclogging the air intake. Try to make sure you clean at least weekly.


We hope the above-mentioned information about the issue of air only blows through defrost vents will be helpful to all the readers. If anybody’s doubts persist feel free to comment in the comment section below. We’ll try to solve your doubts as soon as possible.