While refrigerant recovery is accepted as a fact of life for today’s air conditioning and refrigeration (AC/R) technicians, it remains one of the most time-consuming steps in servicing an AC/R system. This can make it tempting for a technician on a tight schedule to skip the recovery process. However, with the proper understanding of equipment and methods, refrigerant recovery can be faster and easier than venting. Just like tires can affect a car’s performance, the hoses, fittings, manifold, and recovery cylinder all play a role in how quickly and efficiently the recovery process is completed.
Hoses and Hose Fittings
During refrigerant recovery, 1/4″-diameter charging hoses are effectively capillary tubes, greatly reducing flow and potentially causing trouble throughout the process. Quick-disconnect and auto-shutoff hose fittings incorporate valve mechanisms that not only restrict the flow of refrigerant but can act as a metering device during liquid recovery, leading to other problems such as overheating tanks. Using hoses equipped with ball valves meets the Environmental Protection Agency’s (EPA’s) low loss fitting requirement while ensuring full refrigerant flow during the recovery process.
Even when recovering from systems with 1/4″ service valves, using 3/8″-diameter hoses reduces resistance and allows a full flow of refrigerant to reach the recovery machine and, ultimately, the recovery cylinder. Using a shorter length of hose between the recovery machine and cylinder will also reduce the amount of refrigerant released, ensuring de minimis thresholds are not exceeded.
Recovery Cylinder Capacity and Ratings
For safety reasons, it is important to never exceed 80 percent of a recovery cylinder’s rated capacity. In addition to safety, using a cylinder with extra capacity reduces back pressure towards the end of the recovery process, making the EPA’s 10–15 inHg vacuum requirement much easier to reach. For the best results, start with a new recovery cylinder that has already been evacuated below 500 microns. As always, make sure the recovery cylinder is rated for the refrigerant being recovered.
Removing Restrictions for Recovery
“Input restrictions” are points between the AC/R system and the recovery machine that can severely reduce the liquid flow. These points include valve cores, core depressors, restrictive hose fittings, partially-opened manifold valves, and worn-out hoses. A valve core blocks about 90 percent of the inside of an access valve, while a core depressor blocks about 50 percent of the hose fitting. Overheating of the recovery cylinder and high cylinder pressures are often symptoms of input restrictions.
Just like a metering device in the AC/R system, the pressure drop caused by the restriction can result in low-density superheated vapor being fed to the recovery machine. As with an undercharged condensing unit, this limited flow of vapor can render a recovery machine’s condenser useless. When the heat from the recovery machine’s compressor is added, the recovery cylinder is slowly filled with hot vapor refrigerant, increasing back pressure and greatly slowing down the process.
Enabling a full liquid flow to reach the recovery cylinder using 3/8”-diameter hoses will enable better thermal transfer through the cylinder walls and, ultimately, reduce cylinder pressures and temperatures overall.
“Output restrictions” are points between the recovery machine and recovery cylinder that can increase the back pressure on the recovery machine. Damage to the gauges on the recovery machine or loud “knocking” noises during recovery typically indicate a significant output restriction. Both can be symptoms of rapid pressure spikes caused by the output hose being filled faster than it flows into the tank and can also result in significantly reduced recovery speeds.
Just as with the input side, it’s helpful to use larger-diameter hoses and remove unnecessary core depressors. Additionally, connect the output hose from the recovery machine to the vapor port of the recovery cylinder. This allows the refrigerant to quickly empty into the tank, instead of traveling through the liquid port dip tube, which is often smaller than 1/4″ in diameter.
The Greater the Flow, the Faster It Will Go
A recovery machine designed for greater throughput will magnify the symptoms caused by flow restrictions due to greater pressure drops on the input side and higher back pressure on the output side. Buckets of ice only patch up the symptom rather than addressing the causes.
Using larger diameter hoses while removing valve cores and core depressors opens the recovery machine and cylinder up to a full flow of refrigerant, enabling fast, trouble-free refrigerant recovery on every job.
For more information, visit www.appiontools.com.