If your goal is to simply recharge a system that’s low on refrigerant, you can do so without having to know the specific amount that’s required. Simply add enough of the refrigerant specified for your vehicle to bring the level up to the “full” mark on the pressure gauge. However, if you need to replace all of the refrigerant in a system (for example, if it’s been contaminated), you must determine how much refrigerant your car uses so you can add the correct amount. Keep in mind that overcharging or undercharging a system can cause damage, so it’s important to be as accurate as possible. To find out how much refrigerant your car uses, consult its owner’s manual or contact the dealer. Once you have this information, follow these steps: 1) Find out what type of refrigerant your car uses. The three most common types are R-134a, R-12 and R-22. Each type has different pressures and needs different tools for recharging; make sure you have the right kind before beginning. You can usually find this information in the owner’s manual as well. 2) Locate the low-pressure service port on your car A/C system. This is where you’ll attach the charging hose from the kit; it will have a cap with either an “L” or “LP” label on it. If you can’t find it, consult a diagram in the owner’s manual or ask someone at an auto parts store for help. 3) Connect one end of the charging hose from your kit to this low-pressure port and screw it on tightly by hand; then connect the other end of the hose to whichever device came with your kit (usually a canister of pressurized refrigerant). Make sure both connections are secure before proceeding further! 4) Slowly open up whatever valve controls flow from your chosen device into your car A/C system until coolant starts flowing through; then stop and check that everything is still secure before continuing 5) Continue adding coolant until pressure readings on both gauges reach their maximum levels; at this point close off both valves 6) Detach everything (in reverse order from how you attached it), making sure not to spill any leftover coolant 7) Check that all caps are back in place and snugly screwed down 8) Test drive your vehicle briefly with AC turned all way up–if cold air isn’t coming out strong after 10 minutes or so something may still be wrong & repeat process as necessary!