What type of gas should not be used for testing refrigerant systems?

The use of combustible gases for testing refrigerant systems is not advisable because they pose significant safety risks, including the potential for fire and explosion. When testing refrigerant systems, it's essential to use a gas that is non-toxic, non-flammable, and does not react with any of the materials used in the system. Combustible gases can create hazardous conditions in the presence of existing pressures and temperatures inherent in refrigerant systems.

In contrast, gases like neon, helium, and carbon dioxide are non-combustible and can be used safely for leak detection and pressure testing. They are inert and do not pose the same risks as combustible gases, making them suitable for use in these applications. Using the correct type of gas ensures both the safety of the technician and the integrity of the refrigerant system being tested.