The answer is CFC – 22 or HCFC - 22. To locate leaks, it is easily accomplished using a pressure – regulated dry nitrogen charge with CFC – 22. But some technicians prefer to use Refrigerant – 22 (HCFC – 22) to pressurize the system without the use of nitrogen. CFC – 22 is also known as Chlorodifluoromethane. This is a hydrochlorofluorocarbon (HCFC). This is better recognized as HCFC-22, or R-22. It is usually used as a propellant and refrigerant. While HCFC – 22 is also known as class II hydrochlorofluorocarbon refrigerant that is less harmful to the ozone than R -12. If HCFC – 22 is used for leak testing, all refrigerant must be first detached from the system. After the leak test, HCFC – 22 should be remove before putting any other refrigerant. Do not mix refrigerants. Both HCFC – 22 and R -134a fall into the kind of refrigerants known as combustible. If exposed to oxygen, they will burn when under pressure or exposed to high temperatures.