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How to DIY a Car Air Conditioning Recharge

Pressure gauge and can of refrigerant against a background of an open car hood

It is easy to take your car’s air conditioning for granted. Whether or not you used your air conditioning to defog your windshield all winter, you might notice poor performance come spring and summer. After all, you didn’t really need air to be that cold when outdoor temperatures were in the 30s. Fortunately, you can DIY a car air conditioning recharge in about half an hour, saving yourself from a sweltering summer drive. Here’s how to recharge AC car systems in your own driveway.

When You May Need a Car Air Conditioning Recharge

Before a Car Air Conditioning Recharge, Set to Max Cool

Your car’s air conditioning is a sealed system that should not require maintenance. Once the correct amount of refrigerant and oil have been added to the system, they are simply cycled through the components and not actually consumed. Regular usage, as little as ten minutes weekly, is enough to maintain the system. This circulates the oil, lubricating moving parts and conditioning seals, O-rings and hoses. However, if refrigerant seepage occurs, this can result in poor cooling and necessitate an AC refill. You may notice that the air coming from the vents warms up when the vehicle is standing still, or simply isn’t cool at all. Another sign of low refrigerant is icing of the air conditioning lines under the hood. Frosted over air conditioning lines may also leave puddles under the car after the ice melts as a tell-tale clue.

Basic DIY car air conditioning recharge kits include an adapter hose to connect a can of refrigerant (R-134a is the most common today but 1234yf is on the way) to the air conditioning system’s low-side service port. Some DIY AC recharge kits include a pressure gauge with color bars or numbers, while others have temperature-sensitive vent clips. Some kits have leak detection dye, so you can use an ultraviolet light to figure out if there’s any seepage.

How to Perform an Air Conditioning System Recharge

Now it’s time to get to work. Thick gloves and safety glasses are important to protect your hands, face and eyes, as a sudden spray of refrigerant could cause frostbite. Always follow the instructions for your specific DIY car A/C recharge kit, but these general steps on how to recharge car AC will help get your air conditioning ice cold in just a few minutes:

  1. Turn off the engine.
  2. Open the hood.
  3. Find the low side AC port location (it should have a black or blue plastic cap). The low-side port will be on the thicker air conditioning line and is bigger than the high-side port, located on the thinner line. The two service ports are physically different, which helps reduce the possibility of using the wrong one. If there is a cap on the low-side service port remove it now and set it aside.
  4. Pull back on the AC recharge kit connector collar, push the connector onto the port, then release the collar.
  5. Wiggle the connector to be sure it’s fully seated and doesn’t come off.
  6. Start the engine, open the windows and set the air conditioner to “max cold.” If your kit includes temperature clips, insert these into the vents inside the car.
  7. Top off your air conditioning system by shaking the refrigerant can and adding refrigerant in short bursts every few seconds with the trigger or valve.
  8. Watch the pressure gauge or temperature clips, and stop adding refrigerant when the proper pressure or temperature (color) is achieved. Stopping is important because over-charging can cause poor cooling or system damage.
  9. Turn off the engine.
  10. Place the low-side service port cap back on and shut the hood. The service port cap keeps dirt from potentially entering the system at the next service.
  11. The AC refrigerant recharge is complete.

Charging car AC using a DIY recharge kit can get you pretty close to the right system charge level, but for the most accurate (and coldest) AC it can be worth a visit to your local NAPA AutoCare. The machines that a professional shop uses for filling an air conditioning system can provide a precise amount of refrigerant that is hard to measure at home. They can also evacuate the entire system and pull an extremely strong vacuum to ensure there is no atmospheric air left to possibly contaminate the refrigerant, as well as find out why you are losing your AC charge.

When Not to DIY

Recharging a car’s air conditioning can save you a lot of time in the shop, but AC repair can also be a DIYers worst nightmare so consider professional help. Topping off refrigerant can be simple, but something like replacing an AC compressor can necessitate a full system flush along with replacing additional components to fulfill the compressor warranty. There are also strict laws around recharging car AC to prevent environmental damage from the refrigerant . Newer hybrid and electric vehicles with electric motor driven high-voltage air conditioning compressors require special lubricant, which is incompatible with the oil in most DIY air conditioning recharge kits.

Older R-12 systems need retrofitting to run R-134a, and R-134a is incompatible with newer R-1234yf systems. While R-134a refrigerant isn’t as bad a greenhouse gas as R-12, it would be environmentally irresponsible to fill a system with obvious leaks or damage just so it can leak out again. If you have any obvious leaks, bring your car to your local mechanic to get those taken care of first. There are special UV dyes available to help track down AC system leaks so there is no guess work. That way you aren’t wasting a car Freon recharge.

Air Conditioning Recharge FAQ

Question: Does the car need to be running when adding Freon?
Answer: Yes, the engine must be running and the AC compressor engaged for a proper refrigerant refill.

Question: How much Freon does my car need?
Answer: Typically there is a sticker underhold that specifics the proper amount of refrigerant and compressor oil to fill the system.

Question: Can I recharge my car ac myself?
Answer: Yes! Just follow the above directions.

Question: How long does it take to recharge AC?
Answer: An AC recharge can take anywhere from 10 minutes to an hour depending on the method.

Question: Can you mix R12 and R134a?
Answer: Absolutely not. R12 and R134a are very different and are not compatible.

Question: How often do you need to recharge car AC?
Answer: Ideally never, but systems with a small leak may only need to be recharged once a year.

Question: Do you add refrigerant to the high or low side?
Answer: Always add refrigerant to the system low side port

Check out all the air conditioning service and repair kits available on NAPAonline or trust one of our 17,000 NAPA Auto Care locations for routine maintenance and repairs. For more information on how to do a car air conditioning recharge, chat with a knowledgeable expert at your local NAPA Auto Parts store.

Photo courtesy of Pxhere with some alterations.

Benjamin Jerew View All

Ben has been taking things apart since he was 5, and putting them back together again since he was 8. After dabbling in DIY repairs at home and on the farm, he found his calling in the CGCC Automobile Repair program. After he held his ASE CMAT for 10 years, Ben decided he needed a change. Now, he writes on automotive topics across the web and around the world, including new automotive technology, transportation legislation, emissions, fuel economy and auto repair.

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