Why Does Car AC Stops Working on Highway? – 7 Common Reasons!

The car’s air conditioner is a vital component for driving comfortably in a warm climate on the highway. Unfortunately, many car owners end up sweating profusely as their car ac stops working on the highway. Whether you are also the victim or want to prevent it from happening, read on.

In a general car, ac can stop working due to a leaky coolant, a faulty vacuum, evaporator, or a blocked condenser. Let’s look at the most likely causes of car ac malfunctions on the highway and offer simple solutions.

Related Car Air Conditioner: Air Conditioner Only Works When Car Is Moving

Car AC Stops Working on Highway- 7 Common Reason

car ac stopped working suddenly

A car’s air conditioner can malfunction all of a sudden, like other components under the hood. It’s very important to understand what to check to troubleshoot why a car stops working on the highway, fix the error, and avoid further damage. The following are some potential reasons that can prevent a car’s ac from functioning properly.

1. Leak Coolant

Coolant is a vital liquid to regulate a car’s temperature and maintain the required engine temperature for ideal functioning. The car’s AC also requires coolant to run, and if its level drops or the tank runs out, the AC won’t work. Hence, your first step should be checking the coolant level, and then the leakage if the coolant level is okay. In this case, you can use an AC leak finder and black light to find the leak and fix it.

See More: How Much Coolant Loss is Normal? 

2. Vacuum

The next component to check is a vacuum that controls the airflow through the AC evaporator. But a damaged or faulty vacuum can cause the air temperature control flap to redirect airflow through the heater core.

3. Evaporator

Freezing up the evaporator can also prevent your car’s AC from working properly. If the car’s ac sometimes works and sometimes doesn’t, it is an obvious sign of a struggling evaporator. So the next time your car’s a/c stops working all of a sudden, check under the passenger side’s right front. Water condensation should be dripping.

But if you don’t see anything wrong, turn off the ac and turn on the heat. Then recheck after a few minutes. If you see the water streaming, it means the evaporator was frozen up. and it can happen due to a faulty expansion valve or an improper refrigerant charge.

4. Block AC Condenser

If the car’s AC condenser gets blocked, it won’t let the air flow through other parts. Hence, cool air won’t pass through the cabin. As a result, your car’s air conditioning can stop working after 10 minutes. If this is the case, clear the condenser blockage.

5. AC Compressor

The compressor is the main part of a car’s AC. The compressor’s coil cools down the air that flows through the cabin. If the compressor can’t work properly, the car’s engine starts working harder to keep the coil functioning. After a while, the engine may stop working, and the coils won’t function and end up causing the car to stop.

If the failed compressor clutch is causing the problem, you have to replace the clutch with a specialized mechanic. Apart from that, if the dirty compressor can’t generate enough power, take the car to a car wash center. If the compressor still won’t work, let a mechanic diagnose it and repair or replace the affected parts.

See More: Can I Drive My Car With A Bad Ac Compressor

6. AC Thermal Expansion Valve

Does your car’s air conditioning stop working on long trips or while driving at high speeds? Possibly your car’s AC thermal expansion valve is causing the AC system to freeze up at higher speeds or during a long run.

The thermal expansion valve regulates the airflow through evaporation. If the valve struggles to open properly, the system won’t get cold; hence, the orifice will freeze up and won’t be able to control the right amount of airflow through the evaporator.

In this case, you have to check the AC system’s performance to make sure it has sufficient refrigerant or determine if the TXV is causing the problem. The TXV is easy to place after separating from the evaporator; however, a certified technician should handle the operation.

Related Car AC: Car AC Takes A While To Get Cold

7. AC Condenser Fan

The AC condenser is used to keep the AC cool. But if they don’t work properly, the air conditioner will not be able to control the heat inside the car. As a result, your car may stop on the highway. Furthermore, while driving at high speeds, the ac fan, particularly its spindle, may be broken.

This can limit the fan’s motion and slow down or prevent the compressor from producing cool air. Over time, the air conditioner can shut down. Alternatively, while driving at high speeds on the highway, the fan may become loose and eventually cease to function. So if your car’s ac stops working on the highway, it’s a good idea to check its fan.

Also Read: Car Overheats At High Speed Only

Some Handy Car AC maintenance tips to Prevent Stop Working

why do car ac stop working

Maintenance is always the best idea to keep the component in optimum condition, get the best performance, and avoid struggling. The same rule applies to car air conditioning systems and other components. So let’s check out some helpful tips:

Run the ac Periodically on Defrost Mode

Run the car’s air conditioner on defrost mode for around 10 minutes every week on the coolest setting at the highest fan speed. This practice is beneficial in plenty of ways, including maintaining gas pressure, keeping the compressor running properly, cleaning moisture, and preventing mildew buildup. Even in the winter, you should run the a/c to remove humidity and defog the windshield.

Related windshield: What Happens If You Put Windshield Wiper Fluid In Coolant?

Clean the Air Filter

Check, and clean the air filter regularly, and replace it if required. This way, you can avoid bringing dirt into the cabin.

Don’t Pre-Cool the Car

In general, car air conditioning systems operate at peak efficiency while driving. So you don’t need to pre-cool the car. During summer days, place the fan on high while starting the engine and only open the backseat’s window for half a minute to remove the hot air.

Related air conditioning: Subaru Outback Air Conditioning Recharge

Set the AC to the Coldest Setting

Setting the air conditioning to the lowest temperature will ensure the most efficient performance. If it feels cold, adjust the fan based on comfort.

Keep the Car Clean

Bacteria and dirt can have a negative impact on the car’s AC system. So keep the car clean at all times to ensure a pleasant and comfortable environment inside and to avoid any inconvenience. Hence, vacuuming and dusting regularly is a good idea.

Another good practice is to avoid using the a/c in recirculation mode and keep the passenger in the back seat. Otherwise, it may leave stale air behind. This idea works well when the passenger is in front.


1. Who does my Car AC compressor not working but the fan is running?

If the car’s engine works properly but not the compressor, it’s possible that the compressor’s outer unit housing doesn’t receive power. The fan is still working because the central unit is functioning properly. If the compressor doesn’t start, check the wire connection.

2. Why does my Car AC stop working all of a sudden?

Possibly your car’s air conditioning system lost its refrigerant charge. Alternatively, the compressor isn’t engaging during turning on the system because of the electrical fault, and the mat stopped working all of a sudden. The blockage of internal obstructions can also be responsible for this hassle.

3. What if your Car AC stops working after 10 minutes?

If the a/c in your car stops working after driving for a few minutes, find out the underlying reason first. It can happen due to a faulty compressor, getting overheated, stuck blend doors, or a faulty blower motor. To fix the problem, hire an expert mechanic.

Final Words

Unfortunately, the warning light won’t turn on if the car ac stops working on the highway. So after experiencing the problem initially, take the car to the nearest auto shop. Who knows how much this ignorance will cost you. So, once you’ve determined which part is causing ac malfunction on highways, simply troubleshoot to determine the exact cause or leave it to a mechanic. Remember, the more you ignore, the worse it will be for your wallet.