Recovery, Line Set Reuse, and a Vacuum That Won't Hold

Capacity check: maximum net contents = gross limit − tare = 47 − 22 = 25 lb. Current net contents = 36 − 22 = 14 lb. Remaining room = 25 − 14 = 11 lb.

The system holds 6.5 lb, so 11 lb of room is more than enough - proceed with recovery into this cylinder.

Handling rules:

• Never exceed the cylinder's gross weight limit. The 80% fill rule exists because liquid refrigerant expands with temperature; an overfilled cylinder hydrostatic-locks and can rupture.
• Never mix refrigerants in one cylinder. Mixing makes the contents unreclaimable and destroys the reclamation value of the recovered R-22.
• Use only a DOT-approved recovery cylinder in hydrostatic test date, marked for the refrigerant, with the valve and float/level device working.
• Recover, never vent. R-22 is an HCFC controlled under EPA Section 608; venting is prohibited, and recovered R-22 can be recycled/reclaimed and reused.
• Weigh the cylinder continuously (scale, not 'feel'), watch the pressure, and do not exceed rated working pressure. Pull liquid through a throttling device or the recovery machine's liquid port to speed the job, and keep the cylinder out of direct sun.
• If the system is being disposed of rather than repaired, the applicable evacuation requirements still apply before the circuit is opened.

Interpretation: the system reached 520 microns (acceptable only as a starting point; 500 or below is the usual target) and decayed to 2,400 microns in 8 minutes while still climbing. A small, quick rise that then stabilizes at roughly 1,500–2,500 microns typically indicates moisture boiling off under vacuum. A rise that keeps climbing toward atmosphere indicates a leak - a fitting, a Schrader core, a braze joint, or the gauge set itself.

Next test: a standing nitrogen pressure test.

1. Break the vacuum with dry nitrogen to 150–200 psig (never exceed the low-side design pressure or the compressor's rating; isolate the compressor if its rating is lower).
2. Let it stand at least 15–30 minutes (longer for a large system), correcting for ambient temperature change of about 3% per 10°F. A steady drop means a leak.
3. If it holds pressure, the problem is moisture in the system - most likely the old line set, the old coil, or wet oil.

Rule out your own equipment first: a contaminated vacuum gauge, a leaking hose core, or a pump that is not isolated properly will produce the same signature.

Moisture and non-condensables are the two things a vacuum removes, and R-410A systems cannot tolerate either.

• Moisture + POE oil: POE is hygroscopic and hydrolyzes in the presence of water, forming acids. Those acids attack the motor windings' insulation (leading to burnout), promote copper plating on bearings and valves, and create sludge that plugs the filter drier and the TXV inlet screen.
• Freeze-up: residual water can freeze at the metering device and cause intermittent cooling loss that is very hard to diagnose later.
• Non-condensables (air left in the circuit) raise head pressure, increase compressor amp draw and discharge temperature, and reduce capacity - the customer pays for a system that runs hot and short-lived.
• Warranty and liability: manufacturers require documented evacuation (typically 500 microns or below with a decay test) as a condition of compressor warranty. Skipping it transfers the failure risk to you.

So the answer to the homeowner is: the system will run today, but the moisture you leave behind will destroy the compressor, and that is a five-figure conversation neither of you wants. The fix is a nitrogen pressure test to rule out a leak, then triple evacuation with nitrogen sweeps - and, if the drier has been exposed to moisture, replacing it before charging.