Copper tubing is never used with which refrigerant?

Copper tubing is not used with ammonia, which is why it is the correct answer. The primary concern with using copper tubing with ammonia is that ammonia can cause extensive corrosion when it comes into contact with copper and other copper alloys. This corrosion can lead to leaks and system failures, making it unsafe and unreliable in refrigeration systems that utilize ammonia as a refrigerant.

On the other hand, R134A, R410A, and Freon are refrigerants that are compatible with copper tubing. These refrigerants do not have the same corrosive properties as ammonia and can safely operate in systems that utilize copper piping. Thus, the choice of refrigerant and its compatibility with the material of the tubing is crucial for maintaining the efficiency and longevity of refrigeration systems.