Air Only Blows Through Defrost Vents- Reason And Best Fixing Methods

During the harsh winter, the defrost vent plays a very important role in cleaning the condensation stains on the windows and the air ducts inside the car.

Imagine someday having to drive while air only blows through defrost vents. You will certainly have a “freeze” experience in the car and even risk damage to components due to ice and snow.

Our article will tackle this problem with a list of the main causes and the most effective remedies. Follow it to protect your 4-wheeled friend through this cold winter!

Air Only Blows Through Defrost Vents- 7 Main Reasons

Air Only Blows Through Defrost Vents

There are dozens of reasons why air can only flow through defrost vents and not through any other pipes.

Once a test shows that your vehicle is suffering from one of the problems below, it is most likely the leading cause of this problem!

Bad Mode Door Actuator

The mode door actuator controls the air flow through the vent properly. Due to exposure to various sources of dry air, this part is always in a vulnerable state and tends to wear out rapidly over time.

The leading causes of failure associated with the bad mode door actuator include dislodged or broken plastic gears.

Besides, the driver may also encounter application errors such as incorrect wiring, loose installation, and excessive load. If your vehicle has this problem, the front vents will make an annoying click.

Obstructed Air Intake

During driving, air will normally enter the interior through two main routes- the vent (under the fender) and the duct (which circulates the air in the vehicle).

If these get stuck by foreign bodies or have a vacuum leak, then the defroster vents will be the only way air can circulate.

The driver can easily detect signs of obstructed air intake through the smell that lingers inside the car and doesn’t tend to go away (even with the windows open).

This scent obsession affects temperature and air quality throughout the journey, resulting in a worse driving experience than ever before.

Broken Motor Blower

The blower motor is responsible for pushing air through the dash vents. Combined with a blower resistor, it gains an additional ability- controlling the air entering each vent.

When this unit fails, air will not be able to pass through the vent system, resulting in the air only coming out of defrost vents.

Wear, rust, and thermal overload (poor bearings and limited airflow) are the top three causes of trouble.

In the event of a failure, you will smell a burning smell, combined with a shrill noise and slight vibration from the blower motor.

Faulty Blower Resistor

When the driver turns on the air conditioning (AC) or heater, the blower resistor pushes air through the dashboard vents in the cabin.

Besides, it also allows the driver to decide the amount of air to circulate through different fan speeds.

Thermal overload is the leading cause of blower resistor failure. If you have increased the air pressure, but nothing has changed, your blower resistor definitely needs immediate repair.

Faulty Blend Door Actuator

The blend door actuator plays an important role in regulating and controlling the temperature by blocking or allowing air to blow through the heater core.

When this part fails, the top main causes include burnt/broken plastic gears, electric motor burnout, “exhaustion” from overwork, and thermal overload.

To identify the problem with the blend door actuator, you need to pay attention to the temperature in the car every time the AC is on.

The temperature rises and falls erratically, or there is no effective cooling/warming effect. Besides, the driver can detect this problem earlier through the small ticking sound from the vehicle’s dashboard.

Blown Fuse

The fuse monitors the stability of the current and protects the vehicle’s components in the event of a sudden voltage overload.

When the fuse blows, the AC no longer receives power to keep it running and immediately stops working.

You’ll need to check for three main culprits: the ventilation breaker, fan breaker, and clutch breaker.

Usually, no air coming out of defrost only front vents indicates that the ventilation fuse is having problems.

Bad Relay

Relays greatly contribute to regulating the current required for the ventilation system operation. Without help from the relay, the air will have enough momentum to flow through the defrost vents.

Relays always have to operate continuously on / off for a long time, resulting in a much higher rate of wear and tear than other components.

When it has a problem, the blower will not respond to whether to turn on/off the switch or increase/decrease the fan speed.

Alternatively, you can refer to a more manual test method- directly touching the relay. If your finger feels hot, it is a sign that the relay has failed and absorbed too much heat.

How To Fix If AC Only Blows Through Defrost Vents?

How To Fix If AC Only Blows Through Defrost Vents

No one wants to sit inside a car with a bad smell and full of steam on the windows.

Even worse when you have to drive in inclement weather, while the air conditioner does not help regulate the temperature inside the interior.

So, what to do when the AC only blows out of defrost vents and not through any other pipeline?

The answer is that there will be a different repair method depending on the failure’s cause. Follow the fixing methods below for more information!

Fix The Mode Door Actuator

When the mode door actuator fails, the first thing you need to do is unplug it, then clean the mode door actuator thoroughly.

Use your finger to rotate the link shaft inward to check. If the rotation shows smoothness, your mode door actuator is working properly.

Fix The Blower Motor

The driver can promptly detect the blower motor through the noise or strange smell emitted from this part.

During an in-depth inspection, problems were discovered that often included rust, thermal overload, and dirt jamming.

Send your vehicle to a repair center, and the mechanics will take care of the rest for you!

Fix The Relay

Once the relay shows a problem, there is no useful method. The only way for the driver is to get a new one at home or take it to the auto shop for help.

Fix The Blend Door Actuator

If you have trouble with the blend door actuator, it’s best to have a mechanic fix it. Operations related to this part always require extremely high expertise that drivers can hardly perform at home.

Fix The Blower Resistor

If not equipped with repair expertise, a driver certainly cannot perform blower repair, no matter how experienced they are.

Send it to a repair center, and the mechanic will decide if your part will need repair or a new replacement.

Replace A Fuse

When you detect a blown fuse, you must replace it as soon as possible to avoid further damage to the systems it connects.

Since the replacement requires a high level of expertise and special mechanical tools, it is best to seek the help of some qualified professionals instead of doing it yourself at home.

Unclog The Air Intake 

This solution is so easy that anyone can do it at home. Check the air filter to determine the severity of the blockage (dirt, residue, paper debris, leaves, etc.).

Then, clean the intake air using some homemade solutions, or look for it at the department stores in your neighborhood.

Regular cleaning of the air intake at least once a week will limit the dust and dirt in the ventilation system. If the blockage isn’t resolved, go to an auto parts store and buy new air filters.


How Do You Access The Car Vents?

You wouldn’t be able to reach the floor vents without the help of the thumbwheel, which plays a special role in opening and closing the vents.

After fixing the thumbwheel head, rotate it to the right to open it and to the left to complete the vents.

Why Are My Vents Blowing Hot Air?

The vehicle’s actuators regulate the circulating air’s temperature through the driver’s temperature settings.

If these components fail, you will not be able to control the air temperature, resulting in vents blowing hot/cold air.

How Often Should You Unclog The Car Air Vents?

Dirt and moisture accumulate over time inside the dash vents, creating conditions for mold to grow, causing odors, blockages, and damage to the vent system.

Therefore, experts recommend that riders clean this part at least once a month.

Final Verdict

Detecting air only blows through defrost vents can be confusing at first. But now, you have enough useful knowledge about the cause and the most effective way to fix this problem.

The ventilation system has a leading role in controlling air quality and temperature, which directly affects the experience of the driver and passengers.

Therefore, no matter your travel conditions, regular cleaning and maintenance will always ensure this vent system is always operating in its best state.

If you have any inquires or questions, feel free shoot me a message. Wish you will have the best driving experience!

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