Can You Leave A Car Running With AC On? (Find It Now!)

can you leave a car running with ac on

Every car owner usually has something that keeps them up at night concerning their vehicle’s maintenance. One such thing is whether it is okay to leave your car running while the air conditioner is on.

Can You Leave A Car Running With AC On?

It is okay to leave your car running with the air conditioner, provided the cooling system is functioning properly. Air conditioners in modern vehicles have been designed to run all day without causing harm.

Suppose you are in the middle of heavy traffic while heading to work and the weather is so hot. You can safely leave your AC on until you run out of gas or decide to pull over.

How Long Can You Keep Your Car AC On While the Engine Is Running, But the Car Is Parked?

The compressor continuously works to maintain the preferred temperatures if the car AC is on while the engine is running but parked. This compressor will continue working, and the vents will keep producing cold air until the fuel runs out.

Suppose your vehicle’s AC uses 0.20 gallons of fuel every hour and the fuel tank holds 20 gallons. The AC will run continuously for up to 100 hours while the vehicle is parked.

As a car owner, you should avoid turning your AC on when the engine is off, as it will burden the battery.

Suppose you drive your vehicle downtown to meet with a friend and get there first. You are inside the vehicle, but the weather is hot, so you turn on the AC while the engine is off. By doing so, you save gas while cooling your car’s interior.

However, there is a downside to this. Your car’s AC compressor is operated by the serpentine belt that runs through the engine components. This means that if your engine is off, the AC cannot run since the serpentine belt is not turning. Therefore, you are running the blower motor to cool down your car’s interior.

During this time, the blower operates through the car’s battery. The blower motor blows air through the cabin instead of cooling the air. You only feel cool air inside the vehicle because it is constantly in motion rather than remaining still.

As a result, you continue feeling this sensation of coolness until the battery’s charge runs out. Depending on the battery’s strength, this can last for several minutes, hours, or even an entire day.

What Happens If You Leave the Car Running with AC On?

  • If you leave your car running while the AC is on, it will burden the fuel tank instead of the battery. The AC requires fuel to continue producing cold air inside your vehicle. Therefore, the amount of time the AC will remain on will mainly depend on the fuel inside the tank.
  • If you enable the circulation mode, fresh air will pass through the vents until the fuel tank runs empty.
  • On the other hand, if you have not enabled the circulation mode, the AC will recirculate the air inside the vehicle. It is also worth noting that your engine may overheat if you leave your car running with AC on.

If this happens, it signifies that something is seriously wrong. The engine will overheat once you turn on the AC because of compressor overload, an obstructed radiator, malfunctioning cooling fans, a weak water pump, or clogged condenser fins.

If you notice any of these issues, you should take your vehicle to a professional mechanic for fixing it.

Also, exhaust fumes may enter the interior if you leave your car running while the AC is on. These exhaust fumes will likely lead to carbon monoxide poisoning, which can be dangerous if inhaled over a long period.

You may end up suffocating from these fumes if your vehicle does not have adequate ventilation. This explains why many experts discourage car owners from sleeping inside their vehicles, especially if they are running and the AC is on.

However, this issue is irrelevant if you own an electric vehicle since it does not have tailpipe emissions.

What Should You Do the Next Day If You Leave Your Car with AC On?

If you left your car AC on while the engine was running, you want to check whether there is any fuel remaining the next day.

Since the vehicle’s cabin is likely filled with exhaust fumes, you should lower your car windows to let in the fresh air. You will not inhale the toxic carbon monoxide as you drive.

It is also important to take your vehicle to a professional mechanic for inspection. They will ensure everything is functioning well and maybe replace any faulty components.

On the other hand, if you left your car AC running while the engine was off, the chances are that the battery charge has run out. Therefore, the next day you should start driving for about 30 minutes so the battery can fully recharge.

If this is not an option, you should also consider hooking the battery to a charger and allowing it to charge for several hours. Recharging your car’s battery like this will help enhance its lifespan.

Signs of a Failing AC Compressor in a Car  

The air compressor is the most important part of a car’s air conditioning system. Therefore, if the AC compressor goes bad or starts malfunctioning, your car’s AC will not operate as expected. The following are the most common signs of a failing compressor:

  • The AC system blows warm air into the cabin
  • The compressor clutch is not moving as it should
  • Unusual noises coming from the air compressor
  • Broken suction lines
  • Moisture leaks in the compressor
  • Burning rubber smell coming from the engine area
  • Visible wear and tear on the auxiliary drive belt

Do not ignore a failing air compressor as it can lead to health problems for you and your passengers. Additionally, ignoring a failing air compressor will increase repair costs. Therefore, if you notice the above signs, take your vehicle to a professional mechanic for fixing.

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