‘Do I need to set the A/C to zero when switching off my car?’ [Newbie Guide]

Updated Jan 06, 2021 | Same topic: Beginner's Guide

Manually turning it off makes for a good habit.

Many people can’t be bothered with switching off their car’s electrical features prior to turning off the engine. Most (if not all) of these amenities such as the radio and climate control automatically turn off anyway when the engine dies, so the ignition switch acts as a catch-all for everything that runs inside the car.

Xpander Cross aircon

Turning the airconditioning to zero prior to engine shutoff is a good habit to cultivate

As a matter of convenience, there are those who would leave their airconditioning on before killing the engine. The likely belief behind this practice is that it does away with having to turn on the airconditioning again the next time the car is started (as if turning a dial or two was a tedious activity in itself, but we digress).

If you have developed a tendency to leave the aircon switches on between starting and stopping the engine, you might be wondering whether or not it carried serious, long-term consequences for your engine.

Engine start button

Most people prefer a centralized method of switching off electronics a.k.a. the starter button

Your car’s airconditioning/climate control system is composed of two parts: the blower and the thermostat. The former is powered by the electricity stored in the car’s battery, while the latter is enabled by the compressor, which is run directly by the car’s engine through a magnetic clutch.

This is the reason why you can get the fan running even if your ignition is in the ACC (accessory) position, but the engine has to be turned on if you want to cool down the cabin.

While it makes no difference whether the compressor is turned off or on by the engine, leaving the fan blower running places a load on the car’s battery. This normally isn’t an issue when the car has started since the alternator takes over upon ignition, or even when the battery is healthy in standby mode.

But when the battery is close to losing its charge, you’ll need every ounce of juice to crank up the engine, and constantly leaving the fan engaged only takes you that much closer to having a dead battery in your engine bay. And that’s not to mention the mold growing inside the cabin, due to the moisture caused by not giving the aircon vents ample time to dry out before turning off the engine.

>>> Related: 3 DIY tips to deal with moldy smells inside the car vents


The leftover moisture in your aircon provides a good breeding ground for molds in the cabin

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Engaging and disengaging the airconditioning through the ignition switch (as opposed to manually turning it on and off) isn’t going to have any long-term effects on the engine, as today’s compressors don’t sap nearly as much power from the engine as old ones did. But being diligent enough to set the air condition to zero before turning the engine off makes is a good habit to cultivate nonetheless.

We crank out the motoring tips at Philkotse.com.

Joseph Paolo Estabillo

Joseph Paolo Estabillo


Joseph has been a member of various car clubs since he got his driver's license in 2004 – old enough to remember riding in taxicabs with analog meters, but his fascination with cars goes way back. After nearly two decades of working in broadcast media, he shifted gears by coming on board as Philkotse’s first Filipino member and staff writer in 2017.

Apart from his role in Philkotse as Content Team Lead, Joseph has written episodes for Drive, which has been airing on CNN Philippines for five seasons running. He has also delivered content for various car dealerships based in the U.S., spanning multiple brands such as Alfa Romeo, Maserati, Jeep, Dodge, among others.

Keeping his hopes high and his revs low, he dreams about owning a Kei car when he retires. Hates slow parkers.

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