Air Only Blows Through Defrost Vents: How To Repair The Problem In No Time

Imagine you are living the days enjoying the fresh, airy breezes blown from your beloved car on a sunny day. And, one day, you suddenly realize your air conditioner air only blows through defrost vents while the others stop working. Even when you restart the engine, all still function in the wrong direction and cause you lots of confusion.

So to help you with this problem, Car From Japan will now break down the issue for you in the fastest way and share some of the most effective solutions to handle your defrost vent to have a fresh and safe trip.

Air Only Blows Through Defrost Vents: Breakdown The Issue

In general, we can solve any problems related to the car’s ventilation system quite quickly because it is not a complicated issue. Due to high pressure, 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. The airflows outside, when entering the vehicle, will be warmed or cooled by the air conditioner, then spread out the place through air ducts scattered inside the cabin. In the end, these airwaves will then pass through an air vent at the rear to exit, ending a smooth ventilation cycle within the car cabin.

Nowadays, some vehicles also have a different ventilation system installed, where the air recirculates inside the vehicle’s cabin without being blown out. The vents will suck the air out while warming or cooling them again, then blow it back into the car. The system set in this form will be beneficial 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.

car ventilation system
The ventilation process repeats itself in your vehicle non-stop. (Photo:

In seasons with extreme weather such as summer or winter, as we often turn on the air conditioner to keep warm or cool the body when traveling on the road, the ventilation system, particularly air vents, may have to work continuously and led to abuse. Like almost everything, after a long time of use and not properly maintained, they may become clogged, smelly, damaged, and even harm the surrounding automatic parts, whether they are related or not.

Not only is AC blowing through defrost vents, but anything that interferes with the smoothness of the ventilation system when you’re on the road should be noticed and requires intervention to fix in time before they can produce many other uncontrollable harms.

How To Fix AC Stuck On Defrost

Who would ever want to sit in a car filled with clumsy condensation on the windows and smell bad? You may also do not want your beloved air conditioner to fail in the middle of a hot summer or a cold winter.

Defrosting is a vital function that can keep your vehicle from freezing and icing up in cold winters. Moreover, not only is a part of the ventilation system merely working hard to do its job, but the defroster plays an important role when it can affect the smoothness of the temperature control system and the safety and health of the vehicle, as well as the driver.

>> Check out: The Quickest Way To Defrost Your Car With The Defroster

Finding the cause and solution for stubborn stuck defrost vents in advance can save you a ticket to take your car to the garage for a throughout repair and cleaning process. Although the cost of cleaning and fixing a car with a problem with the ventilation system may not be too expensive, it will still waste a lot of time and effort that is not worth it.

With that said, take a closer look at the following causes and solutions for this rather painful car AC stuck on defrost problem right now.

1. Bad Mode Door Actuator

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

Nowadays, many modern door actuator systems have gradually been 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 also always in a vulnerable stage as it is often exposed to air from different raw air sources.

It is a device equipped with gears made of plastic that can easily be broken and slide apart during operation. Not only that, the door actuator can face many problems and operate incorrectly due to overloading, incorrect or confusing wiring, poor quality of incoming air, and even poor mounting.

One of the most noticeable signs that show the mode actuator’s problem is when you turn on the air conditioner, the vent slot in the front will make a click sound, and that is when the air only blows through defrosting vents issue happen. And the next noticeable thing is that you have to find a way to deal with this problem. When the mode door has a hard time working properly, you have to unplug it right away and rotate inside with your fingers.

If your rotation feels smooth and there seem no difficulties running, you can be set free with it. Remember to clean up your car mode door actuator from time to time to ensure it will operate smoothly and effectively during a season with extreme weather if unfortunately encountered.

2. Obstructed Air Intake

Normally, air will enter the car in two main ways, the first is the vents above the dashboard, and the second is the duct where the air is recirculated in the car. If both of the above air blow lines are blocked or obstructed by obstacles, the vehicle will face an issue of AC stuck on defrost, where the air will be concentrated in one vent while unable to escape.

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. All of these above-mentioned direct factors cause blocked vents that you need to deal with right away to avoid long-term hard-to-fix consequences. The filthy vent system will affect the air quality and tempature every time you travel. And no matter how fresh that destination may sound, the polluted car air still brings you a not-so-good experience.

To solve this problem, you should clean and possibly replace the air filters without spending too much time analyzing why the air only blows through defrost vents.

You can completely pump clean air to filter out the pollutants that cause health problems. Not only that, any homemade solutions you can think of for cleaning air intakes are highly recommended to save money, instead of going to the repair shop, as long as it doesn’t damage or break the system.

Try to make sure to clean the air intake at least once a week with specialized cleaning solutions at supermarkets. Although they are just small, simple actions, they will be effective in the long run.

3. Broken Motor Blower

ac only blows through defrost vents
The blower motor is one of the most vital parts of the car ventilation process. (Photo: Auto Repair Guys)

The function of this part is to blow air through the vent. It can also check the amount of air blowing in when combined with a blower motor resistor. With such irreplaceable functions, a damaged blower motor will cause quite a few serious problems for your car. A vehicle operating with a damaged fan motor can not exhaust air through the vents, resulting in no airflow to regulate and balance the air inside the cabin.

The most common problems with the blower motor are corrosion and tearing. As it fails, you can easily spot the problem thanks to the loud hum when you start the air conditioning system, or you will hear an unusual vibration. If you have to travel for a long time and your car operates longer than usual, you may smell a burning smell coming from the air vents due to overload and overheating.

And gradually, starting from a seemingly small part, each component of your engine will be damaged if they often face problems of air restrictions, the most noticeable causes of rust and overheating.

The best way to take care of a damaged blower motor is to identify the causes and deal with the problems. If you don’t want any opponents of the car to suffer from overheating due to air restriction, pay close attention and take good care of the ducts. You should also be careful of rust problems, limiting dirt from entering your blower motor. Promptly fix any leaks in the blower motor if you notice strange smells or noises and change the air filter periodically.

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. When the car AC is stuck on defrost vents, your wind resistor may be faulty and needs intermediate repair.

Thermal overload or overheating is the leading cause of this problem. So, to give the blower resistor total control of airflow rate and strengthen the cabin air, have it replaced at a professional repair shop.

5. Damaged Blend Door Actuator

The function of a blend door actuator is to regulate and control the temperature in the car by permitting or preventing air from passing through the heater core. This part is composed of gears made of plastic, which are quite fragile and unstable. Being made from non-rigid materials will create more opportunities for the blend door actuator to expose exclusively to damaged and broken conditions. Not only that, but this part is also prone to work erratically or even stop functioning when the electric motor is in a state of exhaust caused by excessive and prolonged operations.

Keep an eye on the temperature in your car every time you turn on the air conditioner. If you feel the temperature gradually becomes erratic or not effectively cooling and warming as you have customized the system, your blend door actuator is very likely to have problems that need immediate repair. Before the actuator is completely damaged and cannot be repaired with regular cleaning and maintenance methods, you can easily hear the small ticking noises coming from the dash.

Given the problems that are considered quite serious with this type of actuator, trying to fix it temporarily is not a good idea. However, you can always replace the broken one with a brand new one with just a few basic disassembly and tools. If you are not confident in your mechanic skills, find a reputable repair facility to ensure the system will come back to work smoothly within the fastest time.

6. Blown Fuse In The Ventilation System

The sting of witnessing air only blows through defrost vents in the car can also be triggered by a blown fuse, the part protects the entire ventilation system from dangerous sudden overvoltages (electrical surges). When this unpleasant phenomenon occurs due to a short circuit, electricity will not be able to reach the blower motor, thereby the ventilation system may stop working.

There are 3 types of fuses that you need to pay attention to if encountering the above situation. They are ventilation fuses, fan fuses, and the air conditioner’s compressor magnetic clutch. In general, fuses have the effect of protecting the windings that link the entire electrical circuit or limit the severe explosion cases in the system of your vehicle.

You need to pay attention to monitoring and checking the fuses in the car regularly. If they still blow even after you have just replaced them before, take your vehicle to the nearest repair shop for a comprehensive consultation and review.

7. Bad Relay (Electrical Issue)

ac stuck on defrost
The current required for ventilation is controlled by a relay. (Photo: 1A Auto)

The relay must supply current to the blower motor for it to work. If this does not happen, the ventilation system will be restricted, causing air to be forced through only defrost vents.

Due to the continuous opening and closing acts, the relay is tolerant to wear and tear. And this is also one of the reasons why the blower cannot work properly to ensure the ventilation system in the car does not encounter any obstacles. Another sign of a faulty relay is if you feel warm or hot when you touch it, it indicates that the relay has absorbed too much heat as a result of the breakdown.

Check and replace the relay periodically if you don’t want its problems to add more complications to the entire ventilation system and air quality every time you enter your vehicle.

Wrapping Up

Here are some of the main causes and solutions to the car conditioner’s air only blows through defrost vents problem that we would love to introduce to you today. With the above article, we hope you will understand more about the importance of vehicle ventilation systems as well as air vents for better air quality and good health.

Getting in a stuffy, secretive, and smelly car is something no one wants. So remember to identify the cause and deal with it appropriately to avoid wasting valuable time on fruitless efforts. Take good care of your vehicle’s ventilation system, air conditioner, and all the components that contribute to a great fresh ride. You might be surprised at what a small act of maintenances can do to a car built up with a thousand pieces.

For more updated and helpful car maintenance tips, visit Car From Japan today.