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10 Reasons Why Your Car AC Isn’t Cooling (and Easy DIY Fixes)

I was recently driving around in the deserts of Arizona and my car’s AC system stopped working. I can tell you from experience that this is one of the quickest ways to ruin a commute or a trip. Luckily for me, the fix was pretty easy.

The simple answer is that one or more of the parts of your AC system are acting up. When refrigerant or one of the components isn’t operating at peak efficiency, the air coming out of your vents won’t be as cool as you’d like. The solution depends on the problem. In almost every case, the fix is pretty simple and can be done on your own.

In this guide, I’ll outline 10 reasons why your car’s AC isn’t cooling the way you’d like it to. I’ll also spend some time to outline easy DIY fixes for each reason (when available) and some insight into how your car’s AC works in the first place.

How Your Car’s AC Works

Before diving into why your AC isn’t cool enough, it’s important to understand how your AC system works. Give me a second to talk through this process.

In general, it works identically to how your home’s AC does. It simply takes outside air, sucks the heat out of it, and blows it through vents. But, how does it do that exactly?

Air comes in the front of your car through the grill. There’s a fan that grabs even more air and pushes it inside to a channel of tubes that are coiled. Inside the coil, there’s a refrigerant.

The refrigerant has a single job. It takes the heat out of incoming air and takes it away. This is done by absorbing the energy from the air then scurrying down the line, being replaced by the fresh refrigerant.

The special thing about refrigerant is how good it is at absorbing heat and changing temperature without freezing.

A compressor pushes and pulls the refrigerant along the loop. It’s important to mention that this is all a closed-loop — no new refrigerant is being added each cycle, it’s just getting reused. Without the compressor, the refrigerant can’t do its job.

Now, it’s just a matter of cycling the refrigerant around so the system can get to work. This continues so air is constantly cooled as it comes through your car, and you get cold air out of your vents.

With that out of the way, now I can talk about why your car might not be cooling how you want it to.

10 Reasons Why Your Car AC Isn’t Cooling

It might be hard to know exactly what’s wrong with your AC system before doing some troubleshooting. In this section, I’ll outline some of the more common causes and explain how you can easily fix them on your own.

AC Refrigerant Leak

The refrigerant in your AC system is doing all the cooling. Remember, this is the chemical that sucks the heat out of the incoming air and transfers the energy away. As a result, the air coming out of your vents will be nice and cool.

If the air isn’t so nice or cool, it could be thanks to a refrigerant leak.

Your system requires a certain amount of refrigerant in order to fully cool the incoming air. If you don’t have enough, then you’ll be left with intermittently cool air or lukewarm air.

Testing the AC system for any leaks by measuring the PSI.

It’s worth mentioning that the refrigerant can leak from a number of places. It’s sometimes hard to find the source, but it’s an easy fix once you find it.

Solution: Find the source of the leak. From there, either patch the leak, replace the leaking component or replace the faulty piping. With the leak fixed, fill up your system with more refrigerant and you’ll be golden.

Broken or Blocked Condenser

The condenser is located at the front of your car. It’s a piece that has loops of coolant in it. This is where the air first starts cooling down.

The air passes through the loops of coolant which are coiled vertically on top of each other. If there is a blockage between these coils, then air won’t be able to come through the condenser and cool down.

In addition, the condenser can break. A broken condenser is a lot easier to replace rather than repair. It’s also more expensive, but it’s the only way to truly fix the problem.

Solution: If it’s just a blockage, clear out all the debris by hand. If the condenser is broken, then your best option is to go to a shop and have them replace it.

AC Blower is Broken

On the tail-end of the AC system is a blower. This is a little fan that takes the generated cold air and blows it out of your air vents.

If you noticed that you can crank up the AC power and it’s still not super cool in the cabin, it could be a faulty AC blower.

Vehicle fan blower motor

The quick way to test this is to put your hand up to a vent in your car. Turn the AC speed from the lowest power to the highest power and see if there’s a huge change. If the flow seems weak, you could be due for a blower replacement.

Solution: Remove the plastic panel under your glove box and locate the blower motor. Remove the mounting bolts, take off the blower, and remove the wiring. Grab your brand-new blower and reverse the steps, mounting and wiring it to your car.

Compressor is on the Fritz

The compressor keeps the refrigerant moving around in your AC system. Without a functioning compressor, the refrigerant will sit stagnantly, and the incoming air won’t be cooled at all.

There’s only so much energy that refrigerant can absorb before it doesn’t do anything anymore. This limit will quickly be reached if the refrigerant isn’t cycling around with a functioning compressor.

The result is warm air coming out of your vents.

Solution: Replacing the compressor involves draining and refilling all of the coolant in your AC system. This process is a huge pain in the neck so it’s easiest to have a mechanic do the job for you.

Compressor Belt is Broken

There are a number of different belts in your vehicle. A belt is just a way to take motion from one component and use it to drive another component (giving the new component power).

In the case of your compressor, there’s a belt that gives it power. Over time, the belt will wear down and need a replacement. You’ll notice much warmer air getting blown through your vents once your belt is broken or damaged enough.

AC compressor & belts attached

Solution: Replacing a compressor belt is harder than you might think. I highly recommend having a pro do it since it can involve removing components and draining/ refilling the coolant.

Cabin Air Filter is Clogged

The cabin air filter is a piece that screens out pollen, dust, and debris. It’s positioned right before your air vents to ensure you get the cleanest air possible in your cabin.

Like any other filter, a cabin air filter will get filled with junk over time. The way it works is there are little holes in the filter that only allow particles below a certain size, specifically air, to pass through. Meanwhile, larger particles get left behind and sometimes trapped in the filter.

Once enough is trapped, the level of air that can flow through the filter is minimized.

Your AC system depends on how much air can pass through, so this is an issue. With a clogged filter, not enough air is getting to your vents, let alone cold air.

Solution: A quick change of your cabin air filter is the solution, here. The hardest part is gaining access to the filter. Remove your glove box and open the now-exposed black container. Take out the old filter and put in a new one.

Mold and Mildew

One reason that your car AC isn’t cooling is that mold and mildew are getting in the way. A commonplace to find it is in the car vents.

They’ll collect and block incoming air.

This issue is probably one of the rarer on this list. If you live in especially humid conditions, then you should definitely check for mildew on your vents. In addition, this is more common in vehicles that are older and/ or stored outdoors.

Solution: Use a cleaning agent and wipe down all of your air vents.

A Short Circuit Somewhere

Remember, almost all of your AC system uses electrically powered components. The compressor, condenser, fan, drier, and blower all use electricity.

This means that a single short circuit could ruin the whole AC system. For example, if the compressor shorts, then you’ll get warm air coming out of your car’s vents.

Finding a short circuit is a trickier solution.

Solution: If you have an ammeter and some electrical experience, go through the components of your AC system and test for continuity and power. When you find the faulty component, replace it.

Fuse is Blown

Along the same vein, you could have a blown fuse somewhere. Again, there are a lot of electronics at play in your AC system.

I wrote a whole guide about diagnosing and checking on your car’s fuses (read it here). The bottom line is that fuses blow for a number of different reasons.

Blown car fuse

Once blown, the component won’t work anymore until the fuse is replaced.

Solution: Find the blown fuse and replace it with one of identical resistance.

Engine is Overheating

Finally, an overheating engine could also cause your car’s vents to blow warm air.

The AC system is found in the same bay as your engine. When an engine overheats, a ton of unplanned heat is coming out of it.

When this happens, your AC system will run hotter than usual. As a result, you’ll get hotter air coming out of your vents.

The fact that you’re getting hot air out of your vents is probably the least of your worries with an overheating engine.

Solution: Fix your overheating engine problem before it becomes an even bigger issue.

Conclusion

Now that you can diagnose and fix your car’s AC problem, you should be feeling the cold air on your face in no time. If this guide helped, give me a comment below. Don’t forget to explore the rest of my blog. I also have a list of products that can help any car owner, so check it out.

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Ernest Martynyuk

An automotive enthusiast who's been tinkering with vehicles since I was 15-years old. Repairing automotive electronics has been my main job for over a decade now and have a passion for everything technical regarding cars.

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