Car AC Stops Working When Hot Outside (Why & How To Fix It)

The car’s air conditioner is responsible for cooling and circulating the air inside your vehicle. It does this by removing heat from the air and pumping it back into the cabin. Additionally, it can also help to filter out any dust or pollen that might be floating around in the air outside, making for a cleaner and more pleasant ride.

The car’s AC is one of the most important parts of a car, especially during hot summer days, but sometimes the AC can stop working when it’s unusually hot outside.

The most likely reasons associated with your car AC not working properly is due to evaporator temperature sensor issue, compressor issue, ventilation fan issue, expansion valve issue, being low on freon, and electrical system issue. There are a few other possible reasons that can include a clogged filter or even the thermostat not working properly.

If your car’s AC stopped working when it’s hot outside, you might be wondering about why that is happening, and potential fixes to solve that problem.

But don’t worry, as we’ll be giving you a list of all of the possible reasons why your car’s AC isn’t working properly when it’s too hot out and also a list of possible solutions to fix it.

Why Your AC Stops Working When It’s Hot Outside and More

Here’s a list of the most likely reasons why your car’s AC isn’t working properly when it’s too hot outside:

  • evaporator temperature sensor issue
  • compressor issue
  • ventilation fan issue
  • expansion valve issue
  • being low on freon
  • electrical system issue

If you notice that your car’s AC isn’t working properly when it’s too hot outside, check to see if it’s one of the reasons above.

Air Conditioning System Explained

Expansion Valve

The expansion valve in your car’s AC system is responsible for reducing the pressure of the liquid refrigerant to allow it to expand and reduce its temperature in the process.

The expansion valve helps in maintaining proper pressure and temperature levels within the system, allowing the system to operate smoothly and efficiently.

Without a properly functioning expansion valve, your car’s AC system would not be able to provide the cooled air that you rely on during those hot summer months.


The evaporator in your car’s AC is responsible for absorbing heat from the air inside your vehicle. This process requires liquid refrigerant, which flows through the evaporator coils and absorbs heat as it changes from a liquid to a gas.

The cooled air is then circulated back into the car by the fan. Furthermore, the evaporator also helps to remove moisture from the air, which can improve the air quality inside your car.

Air Compressor

The compressor is responsible for compressing the liquid refrigerant inside your car’s AC, which in turn raises the refrigerant’s temperature and turns it into a gas form. This process picks up the heat from inside your car and deposits it outside, making your car much cooler.

The air compressor is a vital component in any air conditioning system, and without it, your AC wouldn’t be able to do its job properly. So next time you feel cool, comfortable air coming out of your vents, give a little thanks to the humble air compressor.


The condenser in your car’s air conditioner is responsible for cooling and condensing the refrigerant gas back into a liquid. The heat from the refrigerant gas is transferred to the outside air, causing the temperature inside the unit to drop.

As the temperature drops, so does the pressure. Eventually, the condensed refrigerant reaches a point where it can be turned back into a gas and reused in the AC cycle.


The dryer in your car’s AC is a filter that is responsible for removing unnecessary moisture from inside the AC. This is done by passing hot air over a cold coil, which causes the water to condense on the coil and drip into a pan below.

The dryer also collects any lint that may be present in the airflow and deposits it into a small container so that it can be disposed of properly.

Is It Safe To Drive My Car if the AC Stops Working?

While driving if your car’s AC stops working isn’t ideal, it’s not necessarily dangerous. If you need to drive while your car’s AC isn’t working, simply roll down the windows to help keep yourself cool and increase visibility.

If traffic conditions allow, consider pulling over for a bit to give yourself a break from the heat. And of course, make sure you’re staying hydrated by drinking plenty of fluids. If your car doesn’t have power windows or they’re not working properly, opening the vents can help create a cross breeze.

This can be done by adjusting the slats on manual vents or by pressing the “vent” button if your car has one on automatic climate control systems. Just keep in mind that open vents will reduce fuel economy, so you may want to close them back up once you’re out of traffic and moving again at highway speeds.

In most cases, it’s safe to drive without air conditioning, as long as you take some precautions to stay cool and comfortable. So don’t sweat it if your AC goes out, as you can simply just roll down the windows and enjoy the cool breeze from the outside.

Main Causes for AC Not Working

Faulty Evaporator Temperature Sensor

The evaporator temperature sensor is responsible for monitoring the temperature of the evaporator inside your car’s AC, and the most common sign that your evaporator temperature sensor is going bad is when your AC unit isn’t cooling properly.

If you notice that the air coming out of your vents isn’t as cold as it used to be, or if your AC unit seems to be working harder than usual without blowing cool air, then there’s a good chance that your evaporator temp sensor is starting to fail.

In some cases, you may also hear strange noises coming from your AC unit when it’s turned on. Replacing an evaporator temp sensor can vary in price depending on the make and model of your AC unit, but typically runs between $300-$400.

The Compressor Is Broken

When your car’s AC compressor starts to fail, the unit might make unusual noises or vibrate excessively. The air coming from the vents might not be as cold as usual, or the unit may cycle on and off more frequently than normal.

Depending on the type of compressor failure, if the compressor needs to be replaced it will cost around $1,100, making replacement usually more cost-effective in the long run.

The Ventilation Fan Needs To Be Replaced

The ventilation fan inside of your car’s AC is responsible for circulating the air, giving you fresh oxygen to breathe. If your AC is having ventilation issues, the most obvious sign is if the fan breaks down completely and stops running.

Another sign of a problem with the ventilation fan is if it’s making strange noises. If you hear any grinding, clicking, or whirring sounds coming from your AC unit, it’s worth investigating further as these could be indications that something is wrong with the fan blades or motor.

Replacing a faulty ventilation fan in an AC unit can be fairly expensive, depending on the make and model of your unit. However, if you’re only dealing with a faulty fan, replacement costs will typically range from $300-$400.

Faulty Expansion Valve

The expansion valve regulates the flow of refrigerant in the system. If your AC isn’t working as well as it used to, or if it suddenly stops blowing cold air altogether, there’s a good chance that the expansion valve is at fault.

When it goes bad, chaos ensues. Here are a few symptoms indicating a faulty expansion valve:

  • The AC blows warm air instead of cold
  • It takes longer for the AC to cool down a room than it used to
  • The unit cycles on and off more frequently than normal

Replacement prices will vary depending on factors such as the make and model of your particular unit and will usually cost around $150 to $350.

Low on Freon

Freon is the name of a specific brand of refrigerant that your car’s AC might use. If your AC is low on Freon, you may notice the following:

  • The unit isn’t cooling as well as it used to
  • The evaporator coils are frosty or covered in ice
  • There’s a hissing sound coming from the unit when it’s turned on.

Low Freon levels can cause damage to your AC unit, so it’s important to have it checked out by a professional if you think there might be an issue. Replacing the Freon for your car’s AC can cost anywhere from $100-$350 depending on how much is needed and where you live.

Electrical System Problems

The electrical system powers the air conditioner through a system that provides power to run fan motors, as well as other components.

The first and most obvious is if the unit stops working entirely. If you notice strange flickering or dimming lights when the AC is turned on, this could also indicate a problem with the electrical system.

Additionally, if you hear unusual buzzing or humming sounds coming from the AC unit, this could be another sign of an issue. Depending on the severity of the problem, a replacement for the electrical system of your car’s AC can range in price from $160 to $1,000.

Tips To Prevent Your AC From Not Working When It’s Hot Out

Expel The Air Before And During The Drive

One of the main reasons that your car’s AC may not work properly when it’s too hot out is that there isn’t enough air circulating. Expelling the air before and during your drive can help prevent this from happening.

By expelling the air, you are making sure that there is a consistent flow of fresh air entering the car. This will help to keep the temperatures inside more stable and prevents your AC from having to work overtime to cool down the cabin.

Set The AC To Low Mode

When it’s hot out, the last thing you want is for your car’s AC to stop working. But, if you set the AC to low mode, you can help prevent this from happening. Low mode will keep the AC compressor from kicking on as often, which means it won’t have to work as hard and will be less likely to overheat. So next time it’s a scorcher outside, make sure to set your car’s AC accordingly.

Time To Drive

One of the most important things to prevent your car’s AC from not working when it’s too hot out is to drive less. Yes, that’s right – less driving means your car’s AC will have an easier time staying cool.

This is because the engine produces heat while running, and this heat can build up inside the cabin of your car if you’re constantly driving around town, or even just sitting in traffic.

So try to cut down on unnecessary trips and errands during the summer months, and you and your car will both thank you for it.

Change The Components

If your car’s air conditioning isn’t working properly when it’s hot outside, you can try to fix the problem by changing the components in your AC unit. This may include changing the compressor, condenser, or evaporator.

Another thing you can do is check the levels of refrigerant in your AC system and add more if needed. You should also make sure that all of the vents in your car are open so that air can flow freely through them.

Maintenance Service

Poor maintenance can cause the air conditioning inside your car to stop working properly. Debris and dirt build up over time can clog essential components within the system, preventing it from working as efficiently as possible when you need it most.

That’s why regular maintenance service is key to keeping your car’s AC functioning properly all year round – especially during those scorching summer months. By taking proactive measures such as regularly cleaning out debris and checking fluid levels, you can prevent major issues from occurring down the road that could leave you stranded on a hot day with no relief in sight.

So don’t sweat it the next time the temperatures start to rise as long as you make sure your car is scheduled for routine servicing and enjoy cool comfort all season long.

In conclusion, if your car’s AC isn’t working properly due to high engine temperature or the weather being too hot outside, stay calm and don’t worry.

There are a few reasons why this is happening, as well as simple solutions that can help address the issues. By troubleshooting the problem and addressing any underlying issues, you should be able to get your car AC up and running again in no time