Do You Charge AC on High or Low Side?

Servicing your AC system is not something many people decide to do for themselves. Which is fine. But honestly, it is not super hard and can save you some money so why not learn to do it yourself?

This article is going to cover everything you need to know about the basics of the AC system, how that applies to charging the system, how to charge it, and what steps you should take to keep you (and your car) safe.

By the end of this quick blog post, you should feel well-versed in the world of automobile AC and prepared to charge it yourself, if that’s something you still want to do. Let’s get into it right here and now.

On A Cars First Charge Do You Charge AC On High Or Low Side?

When you very first charge the AC unit on your car you must ensure you are charging both the high and low side of the evac system. You must also ensure that the engine is NOT running. This is important to ensure that the refrigerant (the substance that you use to charge the AC) is evenly distributed around the system.

If you fail to balance it within the system there can be a high volume pressure change the first time you start the engine that can blow out parts of the EVAC system and naturally the AC system. The AC system is essentially a closed circuit system so if there are unbalanced or broken seals it will begin to leak very quickly and become almost entirely useless.

Once you have filled the AC system with refrigerant you should ensure that it is sealed on both the low and high sides. If you start the engine and the high side valve hasn’t been resealed then you can say goodbye to your brand-new refrigerant. It won’t necessarily cause a huge amount of damage but it will require you to buy all new refrigerant!

Do You Charge AC On High Or Low Side?

Assuming that this is the second time you have charged the AC system, and have previously ensured it has been filled fully and equally on all sides of the system, you are going to want to charge the AC on the LOW side from now on.

Refrigerant can be quite dangerous if handled incorrectly so it is in your best interest to only charge through the low-side service port. Luckily for you, that’s also far easier to access as it is meant to be accessed with ease. Whether it is accessed by you, your dealership, or a mechanic. The high side of the pressure system is best left alone unless you are filling the AC system for the first time.

If you are charging your AC system for the N’th time but this time it happens to have been drained completely for one reason or another then you should refer to the above section about the charging methods.

Why Should The Engine Be Off When Charging The AC?

To ensure that you don’t have any air in your AC service lines the car should be off at all times. The engine must be running for the AC system to work properly and it will by default start running (to an extent) as soon as you turn the engine on so you won’t be able to safely charge it without killing the engine. It is best to leave the key out of the ignition too, just in case.

Why Does My AC Need To Be Recharged?

Your AC will slowly leak the gasses that keep it cooled over time and they actually become less effective as a refrigerant over time. It is to be expected and not something that you should be overly worried about. You will likely be able to tell when your AC needs to be recharged without your mechanic telling you.

If your AC starts to feel really weak then it’s time to recharge it, Additionally, recharging your AC can improve your fuel efficiency as it requires less fuel and less energy to lower the air temperature. There comes a point when recharging the AC might start to save you a few bucks every time you drive it.

How Do You Find The Low Side Service Port?

The low-side service port is usually located between the compressor and the evaporator that sits on the AC line. The compressor is driven by the fan belt so that should help you narrow the potential location down substantially.

If you really can’t find it you may need to look on YouTube for your particular car’s low-side service port location. Or speak to a mechanic who will be able to locate it for you. You really shouldn’t have too much trouble though as the low side port is quite easy to identify and use. Again, Google and YouTube are your friend and can likely walk you through recharging the AC every step of the way.

How Much Does It Cost To Have Your Car’s AC Charged?

If you decide that you want to recharge your AC yourself it will probably cost you about fifty bucks because you really only need refrigerant. How much you need or how much it costs will vary but fifty dollars is a good benchmark to work from.

If you pay to have it done professionally you can expect the standard kind of markup that mechanics or dealerships typically charge. You should expect to pay about $100 – $150 depending on where you are in the world, etc. However, if you have a luxury car you might end up paying twice that. Be careful.


Hopefully, you now not only know which side (low or high) you need to charge the AC system from when you first charge it and when you are recharging it. It isn’t super complicated and can save you some serious cash over your lifetime if you learn to do it yourself.

Whether or not that’s something you actually decide to do is another matter entirely. Thanks for sticking with us and we hope you got some value out of this article. Goodbye for now.

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