How long does it take for a 12-ounce can of refrigerant to empty into the system?

The time required depends on the pressure difference between the system and the can. When adding refrigerant to a system that is low on charge, cooling of the refrigerant in the can will slow the charging process. Allowing the can to warm to ambient air temperature may improve the charging rate. It will typically take several minutes for a can to transfer into the system. Never use external heat sources to heat refrigerant cans. They may explode and cause serious injury. Please note that some vehicle air conditioning systems have self-diagnostic features that will shut down and lock out the system if the refrigerant charge reaches a pre-determined low level. Do not attempt to re-charge such a system. In this case, the system needs to be serviced by a certified service facility.

I want to recharge my car's system. What tools do I need to charge my system with R-134a?

At minimum you will need a charging hose assembly and a pressure gauge. The charging hose assembly is composed of a can adapter with a piercing valve, a charging hose, and fittings to attach to the AC system. A thermometer is also recommended. These tools are usually offered for sale in the same area in the store as the refrigerant, though not all stores carry all of the tools you might need. In addition, leather gloves and proper eye protection such as safety glasses to protect against incidental contact with refrigerant are strongly recommended. Honeywell also recommends that anyone using Genetron 134a or Genetron 134aUV read and understand the MSDS (Material Safety Data Sheet) prior to use of these chemical products.

Can I add R-134a to a system charged with R-12?

No. Combining these two refrigerants will form a mixture that is higher in pressure than either R-12 or R-134a, and can result in damage to the air conditioning system components, including the compressor, or release of the refrigerant by the system’s pressure relief valve. The hoses and other parts of an R-12 system may not be compatible with R-134a without a proper and complete retrofit that would include removing all of the R-12 refrigerant. The U.S. Environmental Protection Agency (EPA) has passed regulations making the “topping-off” of R-12 systems with R-134a or any other alternative refrigerant illegal.

I want to convert an R-12 air conditioner to use R-134a. Can I open the system and vent the R-12 refrigerant to the air so I can retrofit it?

No. Intentionally venting R-12 or R-134a refrigerant is illegal and a violation of Section 608 of the U.S. Clean Air Act. Also, the EPA mandates that only “Section 609” certified technicians may perform service work on auto AC systems that still contain R-12 and need to be retrofit to other refrigerants. Once a certified technician has removed the R-12 from the system, you can perform your own retrofit.

I tried charging a 12-ounce can of R-134a refrigerant to an AC system, but it would not go in.

Refrigerant will not transfer into the system if the pressure in the system is greater than the pressure in the can. Other possible reasons include, but are not limited to, incomplete or improper positioning of the piercing valve, a faulty, dirty or plugged service port valve, or an unopened valve in the flow path between the can and the service port. Another potential culprit is non-condensable gases (such as air) in the system, a condition that will require a complete evacuation and recharging of the system.

Do I have to drain the mineral oil from the empty R-12 AC system when I convert it to R-134a?

In order to obtain the highest system efficiency and best cooling results, the mineral oil should be drained and replaced with a lubricant recommended by the vehicle manufacturer. If a likely decline in overall system efficiency is acceptable due to cost considerations, then the mineral oil can be left in the system. This oil will ‘park’ in low spots in the system where refrigerant flow is not ample to move it through the system. And "parking" of the mineral oil in the evaporator or condenser can lead to intermittent losses in efficiency.

How much R-134a do I put into an R-12 AC system after it has been retrofit to use R-134a?

The R-134a charge weight should be about 90% of the original R-12 charge weight. The amount of R-12 refrigerant in the system can be found in the service/owners’ manual or on a service plate located in the engine compartment of the vehicle.

How much R-134a do I use to fill an evacuated system?

Again, the amount of R-134a refrigerant in the system can be found in the service manual or on a service plate located in the engine compartment of the vehicle. Most vehicles use between 1.5 and 3 pounds (24 to 48 ounces) of 134a refrigerant.