Low-Pressure Appliance Servicing and Disposal (Type III)
Low-pressure appliance servicing and disposal (Type III)
Type III covers low-pressure appliances, most often centrifugal chillers using R-11, R-123, or similar refrigerants. These systems normally operate below atmospheric pressure, so air and moisture can enter; the exam tests recovery, evacuation to 25 in Hg, purge units, leak detection, and charging safety.
Low-pressure characteristics
Low-pressure refrigerants have low saturation pressures and boil at relatively high temperatures. Because the system runs in a vacuum, any opening can draw in air and moisture. Purge units remove non-condensables, and dehydrating the system is critical. Leak detection may use soap bubbles, electronic detectors, or dry nitrogen pressure testing.
Recovery and evacuation
Use recovery equipment rated for low-pressure refrigerants; high-pressure recovery units may not pull the required vacuum. Recover refrigerant before opening the system. The evacuation target for low-pressure appliances is 25 in Hg vacuum. Never vent refrigerant. Keep recovery cylinders below 80% and do not mix refrigerants.
Charging and safety
Follow the manufacturer's charging procedure. Add refrigerant as liquid or vapor only as specified; never charge liquid into the compressor suction. Use PPE because low-pressure refrigerants can displace oxygen and cause frostbite. Verify purge-unit operation and check for leaks before charging.
Worked example
A 250-lb R-123 chiller needs an evaporator repair. The technician must recover the refrigerant with low-pressure recovery equipment, then evacuate to 25 in Hg vacuum before opening. Using a standard high-pressure recovery unit and stopping at 15 in Hg would not meet the Type III target. After repair, the technician leak-checks, dehydrates, and charges per the manufacturer. The reasoning: R-123 is a low-pressure refrigerant, so Type III rules and the 25-in Hg target apply; venting is illegal.
Traps
Using high-pressure recovery equipment on a chiller. Evacuating only to 15 in Hg or 0 psig. Ignoring the purge unit and non-condensables. Venting R-123 because it is an HCFC. Charging liquid into the compressor suction. Overfilling the recovery cylinder.