You can if you can get your hands on the correct type of refrigerant required for your vehicle. But that is now a major problem for do-it-yourselfers because federal law prohibits the sale of R12 and R134 automotive refrigerants to "noncertified" individuals (to become certified, you must pass a written test approved by the Environmental Protection Agency (EPA) -- something which all professional A/C technicians must do before they can legally work on your vehicle). This rule has been in effect since November 1992.
The law was passed to discourage people from recharging leaky A/C systems. R12 refrigerant, which is used in all vehicles built prior to 1993, is an ozone-depleting chemical. So its sale and use is strictly regulated by the EPA. What's more, production of R12 ends December 31, 1995. After that date, the only R12 that will be available will be that which has already been stockpiled or can be recovered and recycled from existing A/C systems. As the supply dwindles, motorists will be forced to have their A/C systems converted to the new "ozone-safe" R134a refrigerant (a job which may require replacing hoses and other parts depending on the application and model year).
Until late 1994, anyone could still buy refrigerant in large bulk containers. Because of the high cost of such containers, the EPA thought few do-it-yourselfers would buy refrigerant in bulk. But even that loophole has now been plugged. So unless you're a certified professional technician, you can't buy automotive refrigerant period.
This law does not, however, make it illegal to own or use R12 refrigerant. But it does make it very difficult for the average person to obtain it.
Some companies have responded to the "refrigerant shortage" by introducing refrigerant substitutes. Unless such a product is EPA approved, however, it should not be used in your vehicle. Many of these products are flammable, which could create a potentially deadly fire hazard if your A/C system were ruptured during an accident. There is also the problem of "cross-contamination." Federal law requires professional technicians to recover and recycle the old refrigerant in your A/C system when doing A/C repairs. If there's some other kind of refrigerant in your system, it can contaminate their recovery and recycling equipment.
CAUTION: The high side of the A/C system is under considerable pressure. If a can of refrigerant is connected to the high side service fitting, it may explode! The system must therefore be recharged by using the low side service fitting only. If you are not sure which fittings are which, do not attempt to recharge your air conditioner yourself. Wear eye protection and avoid direct contact with the refrigerant as it can cause frostbite on bare skin.
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.