Top-Off at the Strip Mall
You are a Type II technician at a strip mall. A 12.5-ton R-410A packaged rooftop unit has a nameplate charge of 24 lb. The manager reports it has lost cooling twice this summer. You find oily residue at a brazed joint and a suction pressure about 20 psi below normal. The unit was manufactured in 2019. The manager wants you to 'just add a few pounds and come back later' because the store cannot close. You have recovery equipment, nitrogen, and a vacuum pump.
1. Can you legally just top off this system and leave the leak? Explain the leak-repair and venting rules that apply.
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You may not vent refrigerant, but this unit's 24 lb charge is below the 50 lb threshold that triggers the federal leak-repair requirements for appliances. So adding refrigerant without repairing the leak is not automatically prohibited by those leak-repair rules. However, topping off does not fix the leak and may not be good practice. If you open the circuit to repair the joint, you must recover the refrigerant first, then evacuate and recharge. If the charge were 50 lb or more and it were comfort cooling, a leak rate above 15% over 12 months would require repair within 30 days or retrofit/retirement.
2. If you recover the charge to repair the joint, what evacuation level should you meet before recharging?
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This is a high-pressure appliance manufactured after November 15, 1993, so the EPA minimum evacuation level is 10 inches Hg vacuum. For R-410A, manufacturer specifications commonly require a deeper vacuum, often 500 microns, and that deeper specification should be followed. Use dry nitrogen for pressure testing and leak checking, not air. Replace the filter drier if the system was opened, and do not recharge until the vacuum holds.
3. What recovery-cylinder and equipment precautions apply to R-410A here?
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R-410A is a high-pressure blend. Use recovery equipment, hoses, manifolds, and a recovery cylinder rated and labeled for R-410A; do not use a cylinder containing R-22 or an unlabeled cylinder. Recover into the proper cylinder using a scale, and do not exceed 80% of the cylinder's water capacity. Because R-410A is a blend, charge it as a liquid from the cylinder to avoid fractionation, and do not mix recovered R-410A with other refrigerants.