Car AC Blowing Hot Air: Possible Causes and How to Fix Them

Car AC Blowing Hot Air: Possible Causes and How to Fix Them

Is there a better feeling than sitting comfortably inside your own vehicle, safe from the sweltering midday heat, while the cool breeze of your car’s AC chills your veins? Not for our money.

Unfortunately, these air conditioning systems rely on quite a few components to function. If any of these happen to fail, it is likely that your vents will stop blowing out that glorious cool air. It’s easy to let air conditioning problems sneak up on you, especially if you live somewhere where you may not use your AC for long periods of time.

Today, we will go over the top 5 culprits that commonly cause your car’s AC to blow warm air so you can get a grip on the issue before you head to a mechanic. Hey, if you’re handy enough, you might even want to tackle it yourself.

1. Refrigerant Leaks

Refrigerant leaks are the most common reason that a car will fair to blow cold air. Unlike our home air conditioning units, the systems in our cars undergo much more stress from external factors. Along with the vibrations and moving parts of a car during driving, things such as heat, road salt, moisture, accidents, and wear on parts can all cause refrigerant to leak from the system.

Wear and tear on an AC system usually goes unseen. While most of the system is comprised of metal parts, there are some components that are made from rubber that can wear down more quickly. Things such as hoses, gaskets, and seals can unknowingly cause leaks in the system that you may not realize until the system stops blowing cold air.

The most common places for leaks to occur are:

  • O-rings
  • Hose junctions
  • Seals

It is important to note that some refrigerant does leave the system naturally, though it usually does so in minuscule amounts. Leaks in the system can lead to moisture and debris entering and causing corrosion as it mixes with the refrigerant and gets cycled through the system. This can lead to things such as damage to the accumulator and filter, which can be more costly to replace. As such, it’s useful to know how to spot the signs of refrigerant running low.

Mechanics often use a fluorescent dye and blacklight to help diagnose where the leak may be coming from. Once the leak has been found, they can run tests on failing parts and repair damaged components.

2. Electrical Issues

Your car’s AC is operated electronically and is subject to electrical issues. Here are a few to be aware of.

General Wear & Tear

These issues can be the result of many things, such as blown fuses, damaged sensors, and loose connections. Sometimes these issues can be easy to repair, such as replacing a fuse or sensor, but sometimes they can be much harder to repair due to component damage or malfunction.

Climate Control System

There can also be problems with a car’s climate control and associated electronics. Some newer cars come with climate controls built into their control screens, while some have classical controls such as buttons and knobs. Both of these systems send commands to a control module that instructs the heating and cooling system to function accordingly.

These systems are both subject to their associated electrical components failing, such as wiring or contacts. Occasionally the control screens in newer cars can have software issues that can be fixed with a simple reset.

Car Battery

In some cases, the culprit can even be your car’s battery. A dying car battery that is operating at sub-optimal voltage can cause the AC system to malfunction. You may be able to start your car and operate some of the electronics, but if there isn’t enough power in your battery, it may not be able to give enough power to run the compressor properly. If you do need a new battery, here’s where to look.

3. Broken or Blocked Condenser

Every car’s AC system has a condenser that plays a vital role in turning the gaseous refrigerant back into a liquid by removing heat. The condenser is typically located at the front of a car between the radiator and the grill and has a set of fans that cool down its coils to help dissipate the heat.

As the condenser is located at the front of the car, it is subject to numerous factors that can cause damage or malfunction. It is one of the more commonly damaged components during front end collision, as well as from debris from various objects you may encounter on the road. It is also subject to corrosion from things such as road salt and substances in the air, as well as chloride, rain, and fluoride.

Over time a condenser can become dirty or clogged. When this happens, you may notice decreased efficiency in your car’s AC system, or it outright won’t cool the air coming from its vents. When dirt and other debris accumulates on the condenser coils, it can restrict the air from flowing through the coils to dissipate the heat inside the refrigerant.

You may also find that your condenser is leaking refrigerant. Over time the seals on the condenser may wear and cause a pool of refrigerant to leak, or small holes may form from damage that then causes a loss of refrigerant liquid.

4. Worn or Faulty Compressor

Your car’s AC compressor puts refrigerant under high pressure before entering the condenser. It essentially controls the pressure and temperature of the refrigerant and is the first thing that is activated once you turn your car’s AC on. It is driven by a pulley that is often attached to your serpentine belt; wear on the pulley or belt can cause significant stress on your compressor.

A car’s AC compressor endures even more stress than the condenser, and problems with one often cause problems in the other as the components work in tandem. Dirty condenser coils can result in increased temperature and pressure on the system, causing the compressor to constantly run. Blocked suction lines can also cause the same effect.

Inside the compressor, there are also a series of internal components that can become damaged and cause loss of pressure or leaks. The two most common components to fail inside the compressor are the bearings and clutch. If the bearings start going bad, you may hear a high-pitched squealing or grinding noise. The clutch is used to engage drive power to the pulley powering the compressor. If the clutch is stuck, it may not engage or be constantly engaged, causing undue stress on the compressor itself.

If the compressor doesn’t have enough refrigerant, it will typically wear out much faster than normal and usually results in warmer temperatures. This is due to the compressor having to work harder to pump the refrigerant into the condenser.

5. Bad Cooling Fans

Earlier, we mentioned that the condenser has fans that help dissipate heat. If these fans were to go bad then it would be much harder for the AC system to dissipate that heat.

If the fans aren’t running properly, then the refrigerant will leave the condenser and cause warmer temperatures to circulate throughout your car’s AC system. A common symptom of a faulty or failing set of fans is that your car will start running hotter at idle with the AC on as the condenser creates a large amount of heat. Once the car is in motion, it may cool off due to the increased airflow to the condenser.

In more extreme cases, if the fan has failed entirely, you may start smelling a burning scent. As the condenser starts overheating, the components down the line will also begin to overheat. If these components stay overheated, they will become damaged over time, so it’s essential to address the issue right away.


While the warm air blowing from your vents can be a bit of a downer, we suggest you take action rather than hanging tight and waiting for the season to change. Why? Failed components in the system often lead to damage to other components. Even minor issues with a car’s AC can lead to large repair bills if left unattended, so it’s important to take the time to figure out what may be causing the issue either on your own or with the help of a mechanic.

The cost to replace one faulty part will be far less than letting the damage accumulate and having to replace the entire system. This estimate from CostHelper can help you see the difference in the average prices paid for minor and major repairs.

Final Thoughts: How to Keep Your Cool

While it may be difficult to discern what the root of the problem is if you don’t have experience dealing with automotive systems, you’ll at least know when there’s an issue. When you notice a problem, run through our 5 main causes and see if you can find an obvious fault or issue. If you can, great.

Now all that’s left to decide is whether to tackle it yourself or if you should head over to a mechanic. If you opt for the latter, you’ll at least be confident of the issue and won’t need to be worried about over-paying for unnecessary work.

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