Is It Bad to Start Your Car With the AC On?

Let’s be honest. There’s nothing as soothing as blasting the air conditioning system in your car on a hot summer afternoon. The main purpose why these systems are installed in cars is to cool passengers and to make rides comfortable. But like it is with all car appliances, we fail to maintain and take care of the AC. So it’s only natural for you to wonder if it’s bad to start your car with the AC on.

Running your AC compressor at the startup of your car does nothing bad to your car. This is because vehicles nowadays are wired in such a way that whenever you start the engine, the AC compressor clutch is disabled thereby turning off the electrical load of the AC on the engine.

In this article, we are going to discuss in detail why starting your car with the AC on is not necessarily bad. We will also discuss when to turn on the AC, whether it’s bad to have the AC on when your car is parked as well as what happens if you leave the car AC on.

So read on to find out more. This will surely be an enlightening read for you.

Is Starting Your Car With the AC on Bad?

A car’s AC is an electrical device that blows in cool air when in need. The device is driven by the engine. This, therefore, means that if the engine is off, then the AC doesn’t work either.

Most people are confused as to whether they should turn off the AC before turning off the car. If you are one such person and are unsure if starting your car with the AC on is a bad idea, then you need not worry anymore. This article has you covered.

An essential component of an AC system is the compressor. The compressor is what connects the AC to the engine through a cassette wire. This connection only goes live when an engine starts. This is why an AC only works when the engine is running.

Most people believe that the AC consumes much power and fuel when working. Because of this belief, most people get a further belief that if the AC is on when the car is in the ignition, the engine takes on an extra load.

Surprisingly, however, we should mention that it really doesn’t matter if you start your car with the AC still on. The load that will be transferred to your engine is quite minimal and the amount of fuel that will be used is minimal as well. So choosing to turn off the AC when starting your car is ultimately your choice.

Why Starting Your Car With AC On Is Bad

Most vehicles nowadays (automatic cars) are wired in such a way that the AC compressor clutch is disabled during starting the engine. The AC compressor clutches are computer-controlled and they are disengaged automatically when you start your engine. So when you start your engine, the electrical load of your AC is automatically turned off momentarily until the engine is actually running.

For manual cars, on the other hand, the case is a bit different. When you start the car, the AC usually adds on an extra load onto the engine. This is because the AC compressor will kick as soon as the car is started. The load isn’t usually that much to make a huge difference, however.

All in all, the way today’s cars are wired means there’s nothing bad with starting the car with the AC on. When you start the car, the AC will usually gain power after the engine has run for a few seconds. It will therefore be as if you are putting the AC on automatically.

There are exceptions, however. If your battery is new, then you need not worry. In cases where your car battery is old, starting the engine with the AC on is likely to put a load on the engine.

The load on the starter motor would also increase consequentially. So if you have an old car battery, consider turning off the AC before starting your car.

So now that you know there are no problems with starting your car with the AC on, you can breathe a sigh of relief. It really doesn’t matter!

When to Turn On Car AC?

For most people, turning the car AC on is almost a reflex gesture similar to closing your eyes when you sneeze. Most don’t know when to turn on the car AC, which is not


Typically, if your car has been sitting in the sun for a while, you shouldn’t turn on the AC immediately. This is because hot air is usually locked up inside. So when you enter the car, roll down the windows to expel this air out. Once you feel the air is a bit cooler, you can then turn on the AC. This is when you should turn on the AC to your car.

Is It Bad to Have the AC on When the Car Is Parked?

The answer is No. The good news is that cars nowadays are designed in such a way that they can run all day long with the AC on. If the cooling fans are working and sucking air over the radiator into the AC condenser, then it can sit there all day with no harm to your car.

The cops in Houston where there is 198% humidity do this all the time with no harm to their cars. So it’s not bad to have the AC on when the car is parked.

Note that the engine has to be running for you to use the AC. So if you park your car and turn off the engine, the AC will automatically turn off.

What Happens if You Leave the Car AC On?

If you leave the car on idle with the engine running and the AC on, then there will be low airflow through the radiator. If your cooling system is compromised, this may overheat your engine. Other than that there isn’t anything wrong with leaving your car AC on.

If the engine overheats in this scenario, just run it at a high idle until the temperature comes down again. To be safe, just be sure to keep an eye on the temperature gauge. As long as it says normal, your car is fine.

If your engine is off, then your AC will also automatically be turned off. So no need to worry about that score too.

All in all, AC’s are an important element in cars. Just for good measure, consider turning off your AC when starting your car. It won’t do you any harm!

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