Servicing and installing equipment using flammable refrigerants: Assessment of field-made mechanical joints (ASHRAE RP-1808)

This paper presents the results of a study investigating the assembly, durability, and leak rate of mechanical joints used in refrigerant and air-conditioning systems. A significant motivating factor of the study is identifying joint types that are suitable for use in systems that employ flammable refrigerants. In the study, three different fitting types were evaluated (press or crimp fittings, compression fittings, and flare fittings) as well as a set of brazed joints to act as a leak-free baseline. The fittings were asssembled by a combination of experienced and inexperienced technicians, and the assembly times and number of leaks observed after assembly were recorded and compared for different fittings and technician experience levels. All fittings then underwent one type of durability test: Pressure-temperature cycling, freeze-thaw cycling, or vibration testing. The fittings were then leak checked under positive pressure with R32. The results showed the press fittings resulted in the shortest assembly time, fewest assembly errors, fewest failures from harshness testing, and an acceptable leak rate. However, while more prone to failures during assembly and harshness testing, compression and flare fittings, when properly assembled and tightened, resulted in noticeably lower positive-pressure leak rate compared to press fittings.