Air Only Blows Through Defrost Vents: What You Should Do

Imagine you are driving a car, and you turn on the AC. But unfortunately, air only blows through defrost vents, not the main front vents that blow air on your face. This article deals with this problem and how to solve it.

It is frustrating when your AC doesn’t work when you need it to, especially during the hot summer months. There can be many potential reasons why the AC blower vents are not working. 

For example, if the blower motor gets damaged or rusts, air will only blow through defrost vents. Similarly, if the outside air ducts get clogged by bird feathers or seeds, then air cannot circulate properly, affecting the entire ventilation system of the car.

In this article, we discuss these issues and potential solutions.

Air Only Blows Through Defrost Vents

Car AC Stuck On Defrost Vents: What Can You Do?

The car HVAC system sucks air from outside through ducts and grills. It cools the outside air, which flows through the ducts scattered all over the cabin. Finally, the air exits, which blows cool air all over you and the others sitting in the car.

In the summer, the air conditioner might be turned on almost all the time so that you can comfortably drive on the road. The dash vents have to work consistently to comfort you. But so much work can clog the airflow or can cause damage to other components.

When all the AC vents suddenly stop working, and air only blows through defrost vents, it can become extremely uncomfortable for you to drive. It even affects the quality of the air you breathe. 

Let’s look at reasons why air blows only through defrost vents sometimes.

#1. A Bad Relay (Electrical Issue)

The work of the relay is to provide current to the blower motor. The blower motor is the fan that pushes hot or cold air through vents on the dashboard of a car.

But if there is an issue in the relay, the air does not blow from the blower vents, it starts to come out only from defrost vents. The relay can get damaged when it is switched on and off too often, and it affects the entire ventilation system of the car.

Detecting bad relays is easy. If you touch the relay switch and it is too hot, it indicates that it has retained a lot of heat, because of which it is not working effectively. Another way of detecting a bad relay is that the blower motor will not hum. Check the relay from time to time; if it is not functioning, replace it with a new one.

#2. Damaged Blend Door Actuator

The blend door actuator is an electric motor that has plastic gears. It can stop functioning when the blower motor burns out. Additionally, the blend door actuator is quite fragile and breaks easily if you are driving over bad roads.

You should always monitor the temperature after turning the air conditioner on. If it is not cooling properly, you should check the blend door actuator. If the blend door actuator gets damaged. you will hear a clicking or knocking sound when turning on the AC.

You should try to fix it immediately. Delay in repairing will cost you dearly because you will have to replace the actuator with a new one. This component is quite small, you can easily fit it on your palm, so it is also easy to replace.

The blend doors work with the help of a vacuum hose. So, check the vacuum lines thoroughly, and if it’s broken somewhere, then you can fix them using duct tape.  If you aren’t sure where the vacuum lines are, take your car to the nearest service garage to fix it.

#3. A Blown Fuse

The fuse protects your HVAC system from overvoltage spikes. But sometimes, the fuse can blow out because of a short circuit. Hence electricity will be unable to reach the blower motor. Air will blow from defrost vents when the blown motor does not function properly.

There are mainly three types of fuses: fan fuse, ventilation fuse, and compressor magnetic clutch. You need to inspect these fuse from time to time and, if needed, replace them.

#4. Broken Motor Blower

The blower motor is the one that blows hot or cold air according to your temperature settings and fan speed selection. Whenever you change the fan speed, a signal is sent by the resistor to the blower motor, and accordingly, it decides whether to pace up the speed or slow down the speed of the blowers.

But when it gets overheated or the fan blades become damaged, the blower motor does not function. The internal parts of the blower motor might also rust with time, which can cause it to not function properly. The bearings in the motor may also get damaged or rust with time.

Whenever the motor does not work, it restricts the airflow through vents. If you turn on the AC and a burning smell comes from the vents or you hear a strange sound, there may be an issue with the motor.

Air Only Blows Through Defrost Vents

#5. Faulty Blower Resistor

The blower resistor is an electrical component of the ventilation system in the car. The primary function of the blower resistor is to control the fan speed. Whenever you change the fan speed using the knob on your dashboard, the blower resistor changes the setting, further changing the speed of the motor.

When the weather changes a lot, we might end up changing the fan speed settings many times. It puts a lot of stress on the blower resistor, and sometimes, it can get damaged. If the blower resistor gets damaged, the motor will not function properly, stopping the blowers from working.

#6. Bad Mode Door Actuator

The mode door actuator is present in the climate control case. Its primary function is to control which vents will have airflow. The actuator has gears made from plastic. It can break easily. Excess load, poor mount, improper wiring, or poor air quality can also prevent the mode door actuator from functioning properly.

Clean the mode door actuator from time to time so that it will function properly. If you turn the air conditioner and listen to a knocking or clicking sound, that can be because of a faulty mode door actuator, which can cause air to only blow in the defrost vents.

#7. Obstructed Air Intake

Air enters the car through vents above the dashboard and ducts. But if the lines are clogged by fallen leaves, dust, dirt, or any other debris, it affects the car’s ventilation system.

This eventually causes the car to get polluted air, which will not be good for your health. Additionally, air will start blowing from defrost vents because of clogged lines. So, make sure to clean the filters at regular intervals.

Air Only Blows Through Defrost Vents

Frequently Asked Questions

#1. Why is my AC only blowing through defrost vents

Your AC will only blow through defrost vents because of the below possible reasons

  • Problems with the mode door actuator
  • The motor blower is broken
  • Problems in blend door actuator
  • The relay switch is not functioning correctly.
  • There is an obstruction in the air intake ducts.

#2. Why is my AC not blowing out the front vents

When the AC does not blow from front vents, there can be a few possible reasons which you need to investigate. For instance, there can be a blockage in air intake ducts, so air cannot circulate properly.

The blower motor might have become overheated and damaged, and it might not be able to blow cold air through vents. Additionally, if the relay switch is overstressed, then it might not function, which can be why AC does not blow through front vents.

#3. Why is there no air blowing out of the vents in my car

There can be several reasons for air not coming from the car’s vents. For example, the evaporator coils can be frozen, or air filters have gone dirty. The blower motor can get damaged with time, resulting in no air flow from vents.

#4. How do you fix air not coming out of vents?

  • You have to clean the air filters on a fixed interval
  • You have to check AC vents from time to time to ensure there is no obstruction of airflow
  • Check the vacuum lines from time to time.
  • Check the leaks and holes in the HVAC ducts.
  • You must check the fan blades from time to time with a soft cloth.

Wrap Up

We have discussed above most reasons why air blows from defrost vents but not the blower vents. If you face such a situation, investigate the blower motor and all things connected to it.

When air flows through defrost vents, you will end up continuously breathing polluted air, which is not good for your health. Hence it is important to make sure that you do these checks regularly.

Thank you for reading the article!

Photo of author

Sean Mendez

Hi, I am Sean, a self-confessed petrolhead. I live in Boise, Idaho with a busy family of four and our energetic Labrador retriever. Thank you for visiting my website. You can find my email on the contact page.

Leave a Comment