The basic recharging procedure goes as follows: 1. Identify the low side service fitting. 2. Determine the type of refrigerant required by the system. On most 1993 and older vehicles, this would be R12. On most 1994 and newer vehicles, it would be R134a. CAUTION: R12 and R134a refrigerants are incompatible and must not be intermixed. Use the type of refrigerant required for your A/C system only. On most 1993 and newer vehicles, there's an identification decal or sticker that tells what kind of refrigerant is required. Also, the size and design of R134a and R12 service fittings are different to avoid cross-contamination. 3. Connect a can of refrigerant to a gauge set or recharging hose and valve set. Follow the equipment supplier's directions for making the connections. 4. Open the valve momentarily on the gauge set or hose to blow all air out of the line (this is necessary to keep from introducing air and moisture into your A/C system). 5. Connect the gauge set or hose to the low side A/C service fitting on the vehicle. This is usually located near the receiver/drier or accumulator, or suction side of the compressor. 6. CAUTION: Make sure the can of refrigerant is held in the upright position so only vapor enters the line. Do not tip the can sideways or upside down as doing so will allow liquid to enter the low pressure side of the A/C system (This may cause damage to the A/C compressor). Also, never heat the can to make it empty faster as doing so may cause the can to explode. 7. Start the engine and turn the A/C system on high. The compressor should be engaged or cycling on and off (it may be necessary to jump the compressor clutch directly to the battery if the system is extremely low on refrigerant to keep it engaged). Compressor suction will pull refrigerant vapor into the system and slowly empty the can. This can take up to 10 minutes or more, so don't be anxious. 8. When the can is empty, disconnect the charging hose from the service fitting. Use care when disconnecting the "empty" can from the gauge set or charging hose as it may contain some residual refrigerant. 9. Add additional cans of refrigerant as needed until the system is properly charged. CAUTION: The most common mistake made by do-it-yourselfers is overcharging. Too much refrigerant can reduce cooling efficiency just the same as too little refrigerant. To work properly, the A/C system needs just the right amount. Always refer to the system capacity specs in a shop manual or other source to determine how much refrigerant is required. System capacities are specified in ounces. One can of refrigerant equals about 14 oz. Usually three to four cans is enough to fully recharge a typical passenger car A/C system that was empty. If the system is low, one or two cans of refrigerant are usually all that's required.