Which refrigerant has a strong, pungent smell?

Ammonia, known as R-717, is notable for its strong, pungent smell, which is often described as similar to that of urine. This distinctive odor is one of its key identifying features and serves as a warning sign in case of leaks, making it easier to detect and respond to potential safety hazards in refrigeration systems. Ammonia is widely used in industrial applications due to its efficiency in heat absorption and as a refrigerant, despite its strong smell.

The other refrigerants listed, such as R-404A, R-12, and R-134a, have little to no odor or are less noticeable. This makes ammonia distinct in not only its performance as a refrigerant but also in its safety considerations due to its strong smell, which can alert people to the presence of a leak.