Because of the EPA regulations concerning venting and the use of refrigerants for leak testing, the recommended method for leak testing uses a trace amount of HCFC-22 refrigerant mixed with inexpensive dry nitrogen. The system is first pressurized with the trace quantity of HCFC-22 refrigerant to a pressure of about 10 psig. Dry nitrogen is then used to further increase the system pressure to about 125 psig. The trace refrigerant in this mixture is enough to be detected by an electronic leak detector, while the nitrogen provides the system pressure needed to accomplish the test. After the leak testing is completed, EPA regulations allow the mixture of trace refrigerant and nitrogen to be vented to the atmosphere.
Use of the HCFC-22/nitrogen mixture for leak testing is not limited to systems that use HCFC-22. This mixture is also used for testing systems that normally use other refrigerants such as CFC-12, CFC-500, or CFC-502.
Be aware chat EPA regulations prohibit the addition of nitrogen to a charged system for the purpose of leak detection. The system refrigerant must be recovered before the system is pressurized with the recommended trace refrigerant and nitrogen leak-testing mixture. Pure CFCs and HCFCs, when released during leak detection, are considered a violation of the Clean Air Act.
Pressurizing a system with a trace refrigerant (HCFC-22) and dry nitrogen in preparation for leak testing is performed:
• When a system is without a refrigerant charge (empty).
• When a system with a partial charge of refrigerant has insufficient pressure to support leak detection. In this case, the partial charge of refrigerant must first be recovered and then the system pressurized with the refrigerant and nitrogen mixture, as would be done with an empty system.
Pressurizing systems for leak testing using a mix of refrigerant and nitrogen requires that certain precautions be followed:
• Never use oxygen, compressed air, or flammable gas to pressurize a system! A n explosion will result when oil and
oxygen are mixed.
• Nitrogen is a high-pressure gas (about 2,000 psig). A t full cylinder pressure, nitrogen can rupture a refrigerant cylinder and/or the refrigeration system.
• When charging the system with both a refrigerant and nitrogen, always put the refrigerant in first. Valve off and remove the refrigerant cylinder before connecting the nitrogen cylinder.
• To prevent personal injury and control the system test pressure to the safe test pressure limits established by the system manufacturer, connect the nitrogen to the system using a gauge-equipped accurate pressure regulator on the nitrogen tank and a pressure relief valve in the pressure feed line to the system. The relief valve should be adjusted to open at about 2 psi above the system test pressure, but never more than 150 psig. Figure SP-1-3 shows a typical nitrogen pressure regulator system.
• When pressurizing the system in preparation for leak testing, be sure not to exceed the maximum safe test pressures stamp ed on the unit’s name plate or listed in the manufacturer’s service literature for the unit. A safe maximum is 125 psig. Once the test pressure is established, locate any leaks using an electronic leak detector, bubble solution, or both.