How Much Freon Does My Car Need?by Cassandra Cochrun
According to the Environmental Protection Agency, Freon isn't available in the United States anymore because of its adverse effects on the environment. This makes it expensive, and car owners with an air conditioning system that doesn't work properly are faced with the choice to either "top off" the Freon, or use more Freon and evacuate, then recharge the entire system.
Sometimes, you may be low on Freon because there's a small leak in your air conditioning system. If this is the case, you may just add enough Freon to "top off" the system, but you should get the leak fixed immediately so you don't have to waste any more Freon. When you or a mechanic is topping off the air conditioning system with Freon, there isn't an exact way to tell for sure how much Freon is already in the system, or how much more you'll need (reference 1). As a result, topping off will sometimes lead to an over or undercharged air conditioning system (reference 1). Especially if you're topping your air conditioning system off yourself, this method might be cheaper than evacuating the system and refilling it completely, but the EPA warns that many auto shops charge the same fee for both services, so if you're having someone else do it, it might not be cheaper after all (reference 1).
If you decide to extract all the Freon from your air conditioning system, you can charge the system with the precise amount of Freon that your car's manufacturer suggests. While the standard auto air conditioning system needs about three pounds of liquid Freon, the amount does vary, so check with your manufacturer or have your mechanic check.
You may choose to top off or recharge your air conditioning system with Freon yourself, but Mister Fixit warns that Freon is dangerous when mishandled, so you should always wear safety glasses and avoid contact with your skin when working with Freon. If you're topping off the Freon, you should stop adding it when the tubing coming out of the evaporator and going back to the compressor gets very cold and water condenses on it (reference 2). If you're recharging the system yourself, you should know that there are do-it-yourself recharging kits available on the market that include supplies for extracting the Freon, and gauges so that you can judge the level of Freon in your air conditioning system more accurately if you don't know how much the manufacturer recommends (reference 3). For most cars, the system is fully charged when the low pressure gauge reads somewhere between 25 and 40 pounds per square inch (reference 3).