Recovery Cylinder at the 80 Percent Line
A technician is recovering R-134a from a 2015 minivan with a 26-oz charge. The recovery cylinder is a 30-lb DOT cylinder with a tare weight of 13 lb and a water capacity of 30 lb. Its current gross weight is 36 lb. The technician plans to recover the full charge, then use the same cylinder for a second vehicle that needs 2.2 lb recovered. The shop's scale is accurate to 0.5 lb. The technician says, 'The cylinder is rated for 30 lb, so at 36 lb gross I still have 23 lb of room.' The recovery machine's filter-drier was last changed 18 months ago.
1. Calculate the maximum allowable gross weight of the cylinder and determine whether the first vehicle's 26-oz charge can be added. Show your work.
Read the worked answer
The 80% fill limit is based on the cylinder's water capacity: 30 lb × 0.80 = 24 lb of refrigerant maximum. Add tare: 13 lb + 24 lb = 37 lb maximum gross weight. Current gross is 36 lb, so current refrigerant = 36 − 13 = 23 lb. Room = 24 − 23 = 1 lb. The minivan's 26 oz = 1.625 lb, which exceeds the 1-lb room. Therefore the cylinder cannot legally or safely accept the full charge. The technician's '23 lb of room' confuses gross weight with net refrigerant capacity. A fresh or partially emptied cylinder is required.
2. Why is overfilling a recovery cylinder dangerous, and what shop practices prevent it?
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Overfilling reduces the vapor space and can lead to liquid lock, high pressure, and cylinder rupture, especially with temperature rise. DOT cylinders are designed with an 80% limit to allow expansion. Prevent it with a calibrated scale, recording tare and gross weights before and after each job, using a cylinder large enough for the charge, and stopping to swap cylinders before the limit. Never estimate by feel or by the cylinder's nominal rating alone. Keep the scale on a level surface and account for hose weight. If a cylinder is near the limit, recover into a fresh cylinder rather than topping off the overfilled one.
3. The filter-drier was last changed 18 months ago, and the second vehicle needs 2.2 lb recovered. What should the technician do?
Read the worked answer
Do not use the same cylinder for the second vehicle: 2.2 lb exceeds the 1-lb room, and after the first vehicle the cylinder would be over the limit. Change to a properly labeled, in-date recovery cylinder with enough capacity. The filter-drier is overdue; contaminated or moisture-laden refrigerant can damage the machine and carry acid or moisture into the cylinder. Replace the filter-drier according to the manufacturer's interval, and if contamination is suspected, use a separate dirty cylinder and send the refrigerant for reclamation or destruction. Record the cylinder weights and maintenance.