Air Only Blows Through Defrost Vents – 7 Causes

Air Only Blows Through Defrost Vents – 7 Causes

Air Only Blows Through Defrost Vents GÇô Causes

One of the defrost vents’ vital tasks is to clear condensation on the windows.

Imagine driving a car when the only way to get air is through the defrost vents, and other vents aren’t functioning. In this article, we’ll look into the specific causes of such inconvenience.

Reasons Why Air Only Blows Through Defrost Vents

There are various reasons for air only blowing through defrost vents. Let’s a look at them now:

1. Faulty Mode Door Actuator

The main task of the mode door actuator is to control which vents air blows through. 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 the AC is on, and you can hear a clicking sound, your 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. You’re also likely to smell your blower motor burning due to overheating.

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

3. Electrical Issues – Bad Relay

A relay regulates the current needed for ventilation. For the blower motor to operate, the relay must provide the current.

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

The relay wears out very fast due to the stress of constantly switching on and off. You can note when the relay has become faulty by the blower not responding.

A blown fuse can indicate that the relay could not handle the current. Another indicator of a bad relay is when it feels warm to the touch, meaning the relay retained excess heat due to malfunctioning.

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.

You should check the following fuses as they could be the main culprits: fuses for your fans, ventilation fuses, or the compressor magnetic clutch for your AC.

Air blowing through defrost vents only means the fuse for your ventilation is blown.

Your car’s fuse can blow due to a short circuit in the system. If the fuse has a higher amperage than recommended, it will blow.

6. Malfunction Of The 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.

Overheating is usually the leading cause of a failed blower resistor. If you cannot regulate the airflow rate, your blower resistor is damaged, and air will only blow through defrost vents.

Air Only Blows Through Defrost Vents

7. Clogged Air Intake

There are two spots in your car where air can enter:

  • The vents on the lower half of the shield
  • 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.

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

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

Solutions For Your Air Only Blowing Through Defrost Vents

1. 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.

Air will start flowing through the other vents instead of thorough defrost vents only.

2. Take Care Of Your 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.

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.

4. 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.

Replace the blend door actuator if it’s damaged. If you have no confidence in matters of motor repair, get an expert.

5. Repair Or Replace Your Damaged Blower Resistor

A damaged blower resistor’s best course of action is to let a professional mechanic replace it.

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

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 be checked by a professional mechanic.

7. 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 to avoid problems for you and your passengers.

You can use homemade solutions 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.


It is everyone’s goal to have a pleasant vehicle ride. When your ventilation fails, the journey might be highly unpleasant.

Make sure you know why air is only blowing through defrost vents and that you’re using the proper remedy.

It is may be necessary to reach for professional help if you are unfamiliar with automotive concerns.