Recovered Blend in the Wrong Cylinder
You arrive at a 4-ton R-454B split system with a nameplate charge of 9.0 lb. The homeowner reports poor cooling since spring. A previous technician found a leaking Schrader core on the suction service valve, topped off the system twice with vapor from a virgin cylinder, then recovered 6.5 lb into a gray cylinder labeled 'RECOVERED R-410A - 4 LB' that had not been evacuated. The system now shows 25°F superheat at the compressor, low suction pressure, and slight frost at the service valve. The outdoor unit sits on a pad in a side yard at 95°F ambient; the indoor coil is clean with a new filter. You plan to repair the Schrader, evacuate, and recharge. The customer wants to know whether the recovered refrigerant can go back in to save money.
1. What was wrong with the previous service, and can the 6.5 lb in the cylinder be reused?
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Two mistakes. First, vapor-charging a zeotropic blend: R-454B is roughly 69% R-32 and 31% R-1234yf with about 1.5 K glide. Vapor drawn from a cylinder is richer in the more volatile component, so the system composition is now unknown, and 25°F superheat with low suction is consistent with undercharge and/or a wrong mixture. Second, the leak was never repaired, so the system has been losing charge and drawing in moisture.
On top of that, the recovery cylinder previously held R-410A and was not evacuated, so the 6.5 lb is cross-contaminated. It cannot be reused in this or any other system. Do not put it into a virgin cylinder and do not top off with it. Tell the customer plainly that reuse would risk the compressor and would not restore rated capacity.
2. What must be done with the recovered refrigerant and the cylinder?
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Treat the contents as mixed/unknown refrigerant. Label the cylinder clearly (mixed/unknown - do not reuse, with date and your name), keep the valve closed and capped, and confirm the fill is within the cylinder's marked limit - never over 80% of water capacity by weight. Check the DOT requalification date and that the cylinder is marked for the required service pressure.
Send it to a reclaimer with a manifest and keep the paperwork; do not vent it. If the cylinder is out of requalification or cannot be verified, transfer the contents to a compliant cylinder first, using equipment rated for the refrigerant. Point out to the customer that mixing refrigerants can make an entire cylinder unreclaimable, so this mistake has a real cost.
3. Describe the repair, evacuation, and recharge procedure, and how you will verify the charge.
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Replace the Schrader core and cap, torqued to the OEM specification. Pressure-test with dry nitrogen at the OEM test pressure, then evacuate to 500 microns and hold a decay test. Charge by weight as a liquid: use the nameplate 9.0 lb plus the OEM line-set adjustment, on a scale, throttling liquid into the liquid line. Never vapor-charge a blend.
Verify with the OEM charging chart: subcooling at the condenser outlet and superheat at the evaporator at the recorded indoor and outdoor conditions. Record the weights, evacuation levels, and final pressures. If a refrigerant analyzer is available, analyze the new cylinder before charging and record the result; do not analyze and reuse the mixed cylinder. Leave the customer a note that future leaks must be repaired rather than topped off.