Car AC Stops Working When Hot Outside (7 Reasons Why)

On a hot summer day, you need your car air conditioning to work its best. So, what do you do when the car AC stops working when it’s hot outside? If the car AC struggles in hot weather, there are some easy ways to get it working again.

Why Does My AC Stop Working When Hot Outside? (7 Causes & Fixes)

Car AC Stops When Hot Outside

1. The AC Has Excess Moisture And Contaminants

The car air conditioning system cleans out the air and removes the moisture before pumping it back into the cabin. As the debris and moisture build-up in the system, it can prevent the air conditioning from pumping out properly.

One way to prevent this problem is to keep the cabin air filter cleaned. You should replace this at regular intervals, according to the maintenance schedule. If you don’t, you might notice trouble with the air conditioning, as well as some strong odors and difficulty keeping the humidity down. For the cost of a cheap cabin air filter, there’s no reason to neglect this valuable task.

2. The AC Refrigerant Is Running Low

The car refrigerant is what’s needed to keep the air cool. If there are leaks in the system, the refrigerant levels could drop to the point that keeps the cabin from getting cool. If you have the right equipment to test the refrigerant levels, you could check the high and low pressure side to see what’s going on.

Thankfully, it doesn’t cost a lot to pump the system back up, especially if you can do it yourself. In this case, you just need to purchase the cans of refrigerant. If you don’t know how to recharge the refrigerant into the system, you will need to take it to the auto repair shop.

3. The AC Blend Air Door Is Malfunctioning

The blend door actuator uses an electric motor to control the climate control system in your vehicle. It resembles a plastic box that can vary in size and it contains some gears inside.

When the blend air door doesn’t work as it is supposed to, it can’t regulate whether hot or cool air is coming out. As a result, it’s unable to switch between the two. For this reason, you might notice that the air conditioning continues to blow heat instead of cold air. The only way to fix this problem is to replace the blend air door.

4. The AC Compressor Is Not Engaging

If the car air conditioner can’t keep up on hot days, it could be due to the compressor. When the compressor doesn’t operate correctly, there could be several issues causing the problem. For one, it could all be related to the low refrigerant levels. There could also be an electrical issue with the compressor.

There are also times when the compressor can overheat, causing it to fail temporarily. Aside from these problems, the compressor might have failed, requiring a replacement if you want to get cold air again. If you can’t diagnose the different issues, it’s best to have a professional look at the system.

5. The AC Cooling Fan Has Stopped Working

Your vehicle has a cooling fan that is responsible for pushing the air out through the vents. In most cars, there is a multi-speed fan that allows you to adjust how fast the air moves. This fan is controlled by resistors or a computer module. If these parts heat up and burn out, the speed of the air will be affected, leaving you sitting in a hot cabin.

There’s also the possibility that the fan could get stuck on one speed. Either way, you need to replace the cooling fan to get cold air pumping throughout the car cabin again.

6. The AC Condenser Is Broken / Clogged

The air conditioning condenser is a valuable part of the system because it cools down the refrigerant vapors. When the vapor gets to the condenser, it must be cooled down so it can be turned back into a liquid. The condenser itself can get clogged or blocked with debris, significantly reducing its capacity. Additionally, the condenser could go bad, causing trouble with the system.

You can clean the air conditioner condenser, helping it to become more efficient. Otherwise, you might need to replace it to get some cold air once again.

7. The AC In The Vehicle Has Electrical Issues

We have already discussed some possible electrical issues that could cause your problem, such as when the cooling fan fails. You must realize that electrical connections are joining together all of the components of the electrical system. Plus, there are computers and sensors in the system to keep things running smoothly.

If any of the wires or connectors becomes damaged, you could notice trouble with the air conditioning. These problems could also be intermittent. Sadly, it’s one of the hardest problems to diagnose because you must perform a visual inspection of all the wiring until you find the root cause.

Electrical Issues in Car AC

How Does Heat Affect My Car AC?

According to the NHTSA, the interior of the car can reach 115 degrees Fahrenheit when it is only 70 degrees outside. So it’s no wonder it can be so difficult to keep the cabin cool when the temperatures start to rise. The higher the temperature gets outside and the more humidity you are dealing with, the harder your air conditioning needs to work to keep the cabin cooler.

The hot temperatures also put a strain on the car engine because of the extra power needed to run the air conditioning. That’s why it’s important to protect the car’s air conditioning from the dangers of heat and humidity.

Protecting The Car From Heat

If you want to prevent the car AC from not working in hot weather, you can perform some simple maintenance tricks to keep it running better. With just a few minutes and a few bucks, you can avoid costly air conditioning repairs. Follow these guidelines:

  • Run the air conditioner at least once each week for ten minutes. Turn it on the highest fan speed and make sure it is the coolest possible.
  • Run the defrost mode for five to ten minutes a week to prevent mildew from getting into the system.
  • Turn on the air conditioner even when it’s cold out. The setting helps remove the moisture from the car and can help defog the windshield.
  • Check the system for leaks and recharge the refrigerant when needed.
  • Replace the cabin air filter at the specified intervals.
  • Get a comprehensive air conditioning service if you are noticing any trouble.

People Also Ask (FAQ)

Here are common car AC in hot weather questions.

At what temperature do car air conditioners stop working?

The air conditioning system removes humidity from the air, so it works at a variety of temperatures. However, you might see a decrease in efficiency once temperatures get below freezing.

How long should you run a car AC on a hot day?

It’s better to keep the air conditioning running and the cabin cool than to cycle the system. When you turn the AC off, you only allow the humidity to build back up, making it harder to cool down again.

How do you tell if a thermostat is bad in a car?

You will notice trouble with the temperature gauge on the car, acting erratically or leaning to one side over another. The engine could also overheat. If this isn’t dealt with promptly, it could lead to permanent engine damage.


When the car AC is not blowing cold air when it’s hot outside, you are going to be miserable. To fix it, you must first figure out the cause of the problem and then take steps to repair it. Once you are done, you can enjoy the open road once again.

Josh Mitchell

Josh Mitchell

My name is Josh and I am obsessed with DIY and improving my family home. HVAC topics can be tricky for homeowners so I decided to share my knowledge on the subject. When I am not working on DIY projects, you can find me at the beach or my local coffee shop.