Performing an R-134A air conditioning retrofit
By Joe Escobar
What about the older R-12 systems?
With R-12 no longer being produced, the law of supply and demand has resulted in ever-rising prices for the available supplies. It is this price escalation that is forcing aircraft owners to consider retrofits. Scott Steinbach, owner of Waco, Texas-based Steinbach and Associates – a developer of STCs for R-134A conversions (marketed as ConversionAir™) explains: "At this time, there is not a mad rush of owners wishing to convert a normally operating system. Many times, they are opting for a conversion either because the system is not working efficiently, or because of the expense of R-12."
What type of conversion to choose?
Following the manufacturing ban on R-12 and other CFCs, many replacement refrigerants popped up in the marketplace. Although R-134A is the most popular choice for replacement refrigerant, there are other options available. When considering a replacement refrigerant, remember that there is no such thing as a "drop-in" replacement. The EPA requires that the original R-12 must be removed from the system before charging with any alternative refrigerant. This procedure ensures that no cross-contamination occurs. Refrigerants mixed within an air conditioning system could adversely affect performance and may damage the system.
The following information is based on an R-134A retrofit performed by Gary Drapella of JAG Aviation and Scott Steinbach on a Lear 55 owned by American Jet International at the Million Air facility in Houston, Texas. It describes some of the tasks involved with performing the conversion. As with any maintenance task, be sure to follow the specific manufacturers’ procedures.
Before any disassembly is done, a good operational check is in order. Run the system and check for operating pressures. Air circulation should be checked as well as temperature drop. Operate system through all modes including manual and auto as applicable. Note all discrepancies for corrective action.
After operational checks, the R-12 can be recovered. Only an approved recovery/recycling service unit should be used. Remember that all refrigerants have unique service fittings and matching servicing lines. Although this is a way to prevent cross-contamination, it is possible to have incorrect fittings or service lines installed. Care must be taken at all times when working with refrigerants.
After disconnecting the aircraft battery, the recovery cart should be connected to the service ports either on the compressor or on the aircraft plumbing. Ideally, the recovery unit should have a vacuum pump capable of obtaining a pressure on 30-in. Hg vacuum. Evacuate the system for a minimum of 30 minutes after the system has reached a gauge pressure of 28-in. Hg vacuum. Note that altitude will affect obtainable vacuums.
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