Required recovery levels, small appliances and end-of-life equipment

When Northfield finished the grocery rack, Dana did not let Theo disconnect the hoses until the compound gauge showed that the rack had held the required vacuum for fifteen minutes. Then she had him fill in the disposal record and the signed statement the scrap dealer would need before accepting the rack. "That statement is a promise," she said. "It says a certified tech recovered the refrigerant to the required level. The scrap dealer relies on it, EPA relies on it, and your name is on it."

This lesson covers how far a system must be pulled down before it is opened or disposed of, how vacuum is measured for that purpose, the special rules for small appliances, and how refrigerant is handled when equipment reaches the end of its life.

Why there are required levels

No recovery removes every molecule of refrigerant. Some always remains as vapor at the final pressure. The deeper the vacuum, the less is left: a system at atmospheric pressure still holds a full system volume of refrigerant vapor, while a system at a deep vacuum holds only a small fraction of that. A required level sets how much may be left behind, balancing environmental benefit against the time and equipment needed, and it gives technicians and inspectors a clear test: did the system reach the level, and did it stay there?

Required levels are expressed as pressures. Because the amount of vapor left depends on absolute pressure, it is clearest to think in absolute terms, even though many requirements and field gauges use inches of mercury of vacuum, measured from the local atmospheric pressure.

Measuring vacuum

Three scales are used for vacuum in refrigeration work, as RAC-110 explained. A compound gauge reads pressure below atmospheric as inches of mercury vacuum, from 0 at atmospheric pressure to about 30 at a perfect vacuum at sea level. Absolute pressure in millimeters of mercury or kilopascals starts from zero at a perfect vacuum. A micron gauge reads very low absolute pressures in microns of mercury, thousandths of a millimeter; it is used for evacuation before charging, where targets such as 500 microns are common, and is far more precise than a compound gauge near a perfect vacuum.

Inches of vacuum are relative to the local atmosphere, which is lower at altitude and changes with the weather. At sea level the atmosphere is about 29.92 in Hg; in Louisville, at roughly 1,080 ft above sea level, it averages nearer 28.8 in Hg. A gauge that reads 25 inches of vacuum therefore represents a slightly different absolute pressure in different places, which matters little for the moderate levels in most recovery requirements but a great deal for deep evacuation.

Required recovery levels

EPA's Section 608 rules require that, before equipment is opened for major repair or disposed of, its refrigerant be recovered with certified equipment to the levels in the table below, which depend on the refrigerant's pressure class, the size of the charge and when the recovery equipment was manufactured. The technician must verify that the level has been reached before opening the system. For a repair that is not major and after which the system will not be evacuated, the system may instead be pumped down to no higher than 0 psig, and low-pressure systems may be raised to no higher than 0 psig for such work. A system that has a leak, so that the required level cannot be reached without drawing in air and contaminating the refrigerant, is recovered to the lowest level that can be reached without substantial contamination, but not higher than 0 psig, and the leaking component is isolated if possible.

The pattern in the table makes sense once the levels are seen as absolute pressures. Larger charges in larger systems have a larger internal volume, so leaving vapor at atmospheric pressure would waste more refrigerant: they must be pulled lower. Low-pressure systems, such as R-123 chillers, run in a vacuum already, and the vapor left at atmospheric pressure in a large chiller would be a significant mass, so they must be pulled down to a deep absolute level. Very high-pressure refrigerants are an exception the other way: they boil at such low temperatures that pulling a deep vacuum is impractical with ordinary equipment.

# Required recovery levels as absolute pressure, and what is left behind
ATM_SEA_IN = 29.92          # in Hg at sea level
PSI_PER_IN = 0.4912
levels_in_vac = {"0 in Hg vacuum": 0, "4 in Hg vacuum": 4, "10 in Hg vacuum": 10,
                 "15 in Hg vacuum": 15, "25 mm Hg absolute": ATM_SEA_IN - 25 / 25.4}
volume_ft3 = 10.6           # internal volume of a mid-size system
R = 10.73                   # psia ft3 per lb-mol per degree Rankine
molar_mass = 86.5           # R-22, lb per lb-mol
for name, vac in levels_in_vac.items():
    p_abs_psia = (ATM_SEA_IN - vac) * PSI_PER_IN
    left_lb = p_abs_psia * volume_ft3 / (R * 528) * molar_mass   # ideal gas at 68 F
    print(f"{name:18s} -> {p_abs_psia:5.2f} psia, about {left_lb:5.2f} lb of R-22 vapor left in 10.6 ft3")
# The same gauge reading at Louisville's elevation (about 140 m, 460 ft)
atm_louisville_in = 29.4
print(f"10 in Hg vacuum in Louisville = {(atm_louisville_in - 10) * PSI_PER_IN:.2f} psia")

0 in Hg vacuum     -> 14.70 psia, about  2.38 lb of R-22 vapor left in 10.6 ft3
4 in Hg vacuum     -> 12.73 psia, about  2.06 lb of R-22 vapor left in 10.6 ft3
10 in Hg vacuum    ->  9.78 psia, about  1.58 lb of R-22 vapor left in 10.6 ft3
15 in Hg vacuum    ->  7.33 psia, about  1.19 lb of R-22 vapor left in 10.6 ft3
25 mm Hg absolute  ->  0.48 psia, about  0.08 lb of R-22 vapor left in 10.6 ft3
10 in Hg vacuum in Louisville = 9.53 psia

The program shows that a mid-size system at 0 inches of vacuum still holds over two pounds of R-22 vapor, and that pulling it to 10 or 15 inches removes a third to a half of that. At 25 mm Hg absolute, almost nothing is left. On a large chiller, the difference between stopping at atmospheric pressure and pulling a deep vacuum can be tens of pounds.

Small appliances

Small appliances, as EPA defines them, are products that are fully manufactured, charged and hermetically sealed in a factory with 5 pounds or less of refrigerant, such as household refrigerators and freezers, window and packaged terminal air conditioners, dehumidifiers, water coolers and vending machines. For these, the technician must recover, with recovery equipment manufactured on or after November 15, 1993, 90 percent of the refrigerant if the compressor runs or 80 percent if it does not, or evacuate the appliance to 4 inches of mercury vacuum. With older recovery equipment, the requirement is 80 percent or 4 inches of vacuum. These rules are part of the Type I certification.

When the compressor of a small appliance does not run, much of the refrigerant may be dissolved in its oil or trapped on the high side. Access to both the high and low sides, usually with piercing valves on the process tube and the liquid line or the dryer, lets the recovery equipment draw from both. Warming the compressor and tapping it lightly with a rubber mallet helps release refrigerant from the oil. Once the appliance holds at the required level, the access devices can stay on, because the appliance is being scrapped.

Equipment that reaches the end of its life

Old equipment is where much of the remaining ozone-depleting refrigerant sits, and disposal is where it is most easily lost. A refrigerator crushed in a scrap yard, a rooftop unit cut up with a torch or a split system removed by a renovation crew releases its whole charge in seconds. The rules therefore put responsibility on every link in the disposal chain.

EPA's safe disposal rules apply to small appliances, motor vehicle air conditioners and similar equipment, which typically enter the waste stream with their charge intact. The final processor, such as a scrap metal recycler or landfill, must either recover the refrigerant itself, with certified equipment and certified personnel, or verify that it has already been recovered, normally by obtaining a signed statement from the supplier giving the name and address of the person who recovered it and the date, or a contract stating that refrigerant will be removed before delivery. Technicians who dispose of equipment with a full charge of more than 5 and less than 50 pounds must keep records of the recovery. For larger equipment, the required levels in the table apply before disposal.

Before any piece of equipment leaves a job for scrap, Northfield's procedure requires the technician to recover to the required level, confirm the system holds, record the amount recovered and its cylinder, and attach the required notice or statement to the equipment. Equipment with flammable refrigerants gets an additional label warning that it contained a flammable refrigerant and should not be cut with a torch until the refrigerant has been recovered and the circuit vented or purged.

Opening a system after recovery

Once a system has been recovered to the required level, it is opened to air only for the work that needs it. Breaking a vacuum with dry nitrogen, rather than air, keeps moisture out of the system and gives a slight positive pressure so that air does not rush in when the system is opened. Before brazing, nitrogen is flowed through the piping, as Lesson 3 explained. Components that are removed, such as a compressor or a filter-drier, are capped so that moisture and dirt do not enter, and old oil is drained and handled as a waste.

Oil removed from a system contains dissolved refrigerant. It should be drained into a container designed for it, after the system has been recovered, and the refrigerant allowed to come out of it into the recovery system rather than the air. Used refrigerant oil is regulated as a waste in many states and goes to an oil recycler.

Systems that trap refrigerant

Some systems hide refrigerant from the recovery machine. Heat pumps have a reversing valve and check valves that can isolate parts of the circuit, and an accumulator on the suction side that holds liquid and oil; recover from both the liquid and suction service valves, and expect the accumulator to give up its refrigerant slowly. Systems with liquid line solenoid valves can trap liquid between the solenoid and the metering device when the solenoid is closed, so the solenoid should be opened, electrically or with its manual stem, during recovery. Systems with several evaporators or compressors, such as racks, have isolation valves, crankcase oil and branch lines that each need attention.

Cold is the other trap. Refrigerant in a coil sitting in a cold space, such as a freezer evaporator or an outdoor condenser in winter, has a low pressure, so it boils off very slowly. Warming that part of the system, by running fans or defrost heaters where it is safe to do so, or waiting for warmer conditions, often does more to finish the job than running the recovery machine longer.