So your AC is blowing warm, and you know you need a refrigerant charge, but how much should you buy? And considering that both too much and too little refrigerant will make the system not work properly, how much should you add to your system?
That’s a loaded question.
Most cars hold between 28 and 32 ounces of refrigerant (or about 2—3 12oz cans), however larger vehicles and those with rear A/C will likely hold more. Check your vehicle manual for the system capacity for your specific vehicle. Remember, though, that there will likely be some refrigerant left in your system so you will not be required to install the full capacity of refrigerant each time. Unfortunately, there is no way to measure the amount that actually remains. Another important consideration is that refrigerant cans don’t indicate how much is left in them after you do a partial charge. So if you buy a 22 oz can it’s difficult to determine whether you’ve added 6 oz, 12 oz, or 19 oz.
Usually an A/C system isn’t cooling properly due to a small leak in the rubber components, and a refrigerant charge, especially one with a leak sealer or O-ring conditioner, will be enough to get you through the season. However, in other cases (body damage, for example), there could be a larger leak in the metal components. The best option would always be to remove and recover all the refrigerant that remains in the system, repair the leak, and charge it with the precise amount that your OEM recommends.
When that is not possible, it’s good to know that with a little bit of knowledge, and the proper tools and equipment, you can get the job done without worry of over– or under-charging your system.
A manifold gauge set will help to measure the psi’s in the system. The gauge will help identify when the system is adequately pressurized. For a good charge, the low-pressure gauge should read between 25 and 40 psi (pounds per square inch), and the high pressure gauge should read between 225 and 250 psi. Another useful tool is a refrigerant scale. A scale will allows you to know how much refrigerant (by weight) was actually added. You can also use a thermometer on your dashboard vents to test the temperature of the air coming out during a recharge. When everything is working properly your A/C system on max cool should be blowing out air that is around 38-48 degrees F. An A/C system is comprised of a variety of components, hoses and fittings that circulate and pressurize refrigerant. Understanding the system as well as the steps for a refrigerant re-charge will keep your system from being over– or under-pressurized.