Rooftop Unit Leak Rate and Repair Deadline
A 20-ton rooftop packaged air-conditioning unit uses R-410A and has a nameplate charge of 32 lb. The unit serves a comfort-cooling space. Over the past 12 months, a technician has added 8 lb of R-410A during three service calls. A leak is now found at a brazed elbow in the evaporator coil. The building owner asks whether repair is mandatory and how quickly it must be done. The technician plans to recover the remaining charge, repair the leak, evacuate, and recharge. The technician has a recovery machine, a vacuum pump, and a micron gauge. The appliance is not a small appliance because its charge exceeds 5 lb. The technician must determine the leak rate, the applicable leak-repair threshold, and the correct evacuation level. The owner is worried about downtime and wants to know if a retrofit or retirement plan could extend the deadline.
1. Calculate the leak rate and determine whether the appliance exceeds the leak-repair threshold for comfort cooling.
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Leak rate = refrigerant added over 12 months ÷ full charge = 8 lb ÷ 32 lb = 0.25, or 25%. For comfort-cooling appliances containing 5 lb or more, the leak-repair threshold is 30% annualized. Because 25% is below 30%, the appliance does not exceed the threshold, so mandatory leak repair under the leak-repair rule is not triggered at this time. However, the technician should continue to monitor and record refrigerant additions. If the leak rate later reaches 30% or more over a 12-month period, repair would be required. The calculation must use the full charge and the 12-month period; using only the last service call would be incorrect.
2. If the leak rate had been 35%, what repair deadline would apply, and what alternatives exist?
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If the annualized leak rate were 35%, the owner would be required to repair the leak within 30 days of discovering the exceedance. Alternatively, the owner could develop a retrofit or retirement plan within 30 days and complete the retrofit or retirement within 120 days. The owner must also verify the repair within 30 days after the repair is completed, or within 30 days after the retrofit or retirement plan is completed. The technician should document the leak rate calculation and the repair date. Because this is a comfort-cooling appliance, the 30% threshold applies, not the 10% commercial-refrigeration or 20% industrial-process threshold.
3. What evacuation level must the technician reach before recharging, and why is a micron gauge needed?
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The technician must evacuate the system to 500 microns or lower before recharging. A micron gauge is needed because manifold gauge pressure readings are not precise enough at deep vacuum; they cannot distinguish 500 microns from 2,000 microns. Proper evacuation removes moisture and non-condensables that could form acids or cause higher head pressure. The technician should also use a vacuum pump with a fresh oil charge and isolate the pump from the system after evacuation to verify the vacuum holds. For a high-pressure appliance of this size, 500 microns is the applicable target.