Why is My Car AC Blowing Hot Air? | Autance

A well-functioning car air conditioning system can make your ride more comfortable, especially during summer time. If you’re stuck in…

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Why is My Car AC Blowing Hot Air? | Autance © Why is My Car AC Blowing Hot Air? | Autance

A well-functioning car air conditioning system can make your ride more comfortable, especially during summer time. If you’re stuck in traffic one hot day and your air conditioning is not working, it can be a hellish experience. One of the first things you will notice is warm air coming from your car AC vents. You know that there’s a problem but what could be causing your AC to blow hot air?

Low Refrigerant Levels

The most common cause of hot air coming from car AC vents is low levels of refrigerant. This is a substance that provides the means upon which the system can get rid of excess heat and provide the necessary element for cooling the passenger compartment.

If there is insufficient refrigerant circulating in the car AC system, then it will not be able to get rid of the excess heat. Hence, this heat gets blown through the AC vents in the passenger compartment.

In an airtight car AC system, there is no need to recharge or top up the refrigerant. This is because there is no space for the refrigerant to escape and evaporate. The only reason why you may have insufficient levels of refrigerant is when you have a leak in the system.

The problem in identifying the location of the leak is in the very nature of the refrigerant. As it goes out of its canister, it is often in a gaseous state. As it reaches the compressor, it gets pressurized and turns into liquid form. It then enters the condenser where the liquid refrigerant gives off excess heat. From here, the refrigerant turns into a gaseous state again before reaching the evaporator.

As you can see, refrigerant has the uncanny ability to turn into a gaseous state the moment it meets an area of less pressure or resistance. Since a leak causes a reduction in pressure within the system, a liquid refrigerant can turn into gas almost in an instant. This makes it quite challenging to determine where the leak is.

It can occur anywhere in the connections or hoses of the system. It can also occur in the compressor, the condenser, or the evaporator. The point is that ordinary vehicle owners will have a hard time determining the exact location of the leak. Hence, only a professional car air conditioning technician can help solve the problem.

Related Post: Best Car AC Refrigerants

Problems in the Condenser

The main job of the condenser is to remove heat from the liquid refrigerant coming from the compressor. This allows the liquid to “cool” down before it converts again into gas as it moves through the rest of the AC system. The condenser looks like a smaller version of the radiator. Right in front of it is a pair of cooling fans that help to remove the heat from the liquid refrigerant.

There are two main issues in the condenser that can lead to a car AC system blowing hot air. The first is a blockage anywhere in the series of tubes in the condenser. Any degree of blockage in the system can lead to the condenser not being able to execute its principal function. Hot liquid refrigerant stays hot. As such, you can expect the air flow in the passenger cabin to be hot, too.

The other problem is related to a broken condenser. A puncture in any of the tubes of the condenser can lead to a leaking refrigerant. If there is no leak, it is still possible to break the condenser altogether. This leads to a loss of its fundamental function.

Addressing blockage often requires flushing of the system by a trained AC technician. If the condenser is already broken, there is nothing left to do than to replace it with a new one.

Faulty Compressor

Considered as the heart of the modern car AC system, the compressor is what drives the refrigerant throughout the series of tubes, hoses, and interconnected devices. Without it, it would be impossible to move the refrigerant. You will still get air flow through the AC vents in the passenger compartment because of the fans in this section. Do not expect the air do be cold, however.

One of the main reasons why a compressor may fail is if it was not used for a very long time. Starting it shocks the system and can hasten the speed of its deterioration. One way to keep your compressor in tip-top shape is by running your AC on full blast for 10 to 15 minutes once a month, regardless of the ambient temperatures outside.

Broken Cooling Fans

We mentioned above that the condenser often has a pair of cooling fans in front that aid in the removal of heat from the liquid refrigerant. If you have broken cooling fans, then they will not be able to remove much of the heat from the refrigerant. The air you get inside the car is not as hot as a faulty condenser, however. It is still enough to make you sweat, nevertheless.

Cooling fans are not the sturdiest components in a modern vehicle. They can crack if hit by a road debris. The only recourse for cracked cooling fans is to replace it. Other potential causes of a problem in the cooling fan are a blown fuse and some other electrical problem.

Electrical Problems

The different components that run the car AC system requires electricity to operate. The problem is that it is not always easy to diagnose an electrical problem. One has to follow the wires from the fuse box all the way to the individual AC components. Many of these wires are also obscured by other automotive parts.

You can inspect those wires that you can reach. If there are signs of damage, it is possible to mend the wires. If this doesn’t solve the problem, then having an auto electrician identify the electrical issue can help.

Hot air coming from your car AC vents can mean that you have low levels of refrigerant. It can also be due to a problem in the condenser, the compressor, the cooling fan, or the electrical system of your car.


  1. How Automotive Air Conditioning Works – HowStuffWorks
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