Refrigerant Recovery.

[jeff5may]

I included a pic in post #10 of 99% of what I use usually. I have found that there is an abundance of used refrigerators sitting idle in garages and barns everywhere, free for the asking. The condenser assemblies of the compact, high-density hx type are made to be removed and replaced as an assembly, so very little modification is necessary to morph the extracted unit into a recovery device.

Starting with an old refrigerator that still has a charge, I install a piercing valve near the end of the "extra" tube leaving the compressor, whose end is crimped off and brazed. This is the factory service port, and is connected to the discharge of the compressor. I connect the piercing valve to the high-side hose of my refrigerant gauge set and purge the high-side and center hoses. The center hose is then connected to the recovery cylinder on a scale. I prop the freezer door open and get everything situated to start recovering refrigerant. At this point, the high-side valve on the gauge set and the valve on the recovery cylinder are verified to be closed.

I then plug the refrigerator in and let it try to do its job cooling. I watch the gauge and wait for the pressure to stabilize while double checking for leaks in the recovery rig. An easy way to do this is to cap the low-side end of the gauge set and open the low-side valve on the gauge, then crack open the recovery cylinder briefly (this will not work with a cylinder with a vacuum drawn on it). If the pressure changes after the cylinder is closed, there is a leak. Leaks are bad. Check, check, and check again. Once the unit warms up and stabilizes, the valve on the recovery cylinder can be opened, and the compressor will be ready to pump refrigerant into the recovery cylinder. I tare out the scale at this point.

To initiate recovery, crack the high-side valve open slightly. The liquid stored in the bottom of the compressor and the condenser will be forced into the recovery cylinder if you open the valve too much or too fast. It won't hurt the compressor, but the pro's do it slowly, as oil will travel with the boiling refrigerant into the recovery cylinder. The cap tube in the refrigerator passes very little mass, but allows a little gas to flow back to the suction side of the circuit, so the compressor gets some cooling until nearly all the liquid is recovered. The scale will register the amount of refrigerant recovered.

Once the vast majority of the refrigerant has been recovered, the scale will stop registering an increase in weight. At this point, the valves may be closed, and the compressor may be shut off. The system pressure will drop as the cap tube equalizes the high and low side pressures. The remaining tidbit of gas remaining can be vented when the hose is disconnected from the piercing valve.

It is pretty fruitless to try to recover the last gram or less of remaining refrigerant, but the ice bucket method can be employed here with success. The cap tube can be crimped to further restrict flow. To force a vacuum to build up in the evaporator, the compressor is energized briefly. The high-side pressure will build up, then drop to a lower value as the high side valve is opened and shut, and the remaining gas condenses in the recovery cylinder. The low-side valve trick mentioned before can be employed to register the pressure difference between the recovery cylinder and the refrigerator. When the high-side valve is shut and the compressor is de-energized, the system pressure will fall to a lower value if the cap tube didn't get completely crimped shut.

If you don't want to braze, the refrigerant lines can be cut at strategic places on the suction and liquid lines that are easy to flare. All of the units I have extracted have electrical connectors leading to the rest of the refrigerator, so besides a few screws and the refrigerant tubing there's nothing else to remove. When the assembly is removed, you have a power source and neutral wire, as well as a thermostat loop (at the least), available to assume control. You have a suction line, a gas discharge line, and a liquid line available, with the condenser and its fan acting as a gas/liquid separator. The thing can be used with a few flare nuts and fittings added, or can be custom-built to your heart's content.