Since the new R-134a refrigerant type replaced R-12 in vehicles and supply stores, owners of cars designed to use the older type have been in something of a dilemma. Many owners, to offset the difficulty in obtaining R-12 nowadays, innocently took the opportunity to install a do-it-yourself "converter kit." This kit promised to allow the use of R-134a but conveniently forgot to mention all the complications of the switch. If you obtained your Mercedes from someone who used one of these do-it-yourself kits to allow the use of R-134a, many components of the system may decide to act up. Here are four reasons such a system could be malfunctioning.
1. Failure to completely flush the system first
The PAG compressor oil used for R-12 is not compatible with the mineral oil used with R-134a. If the person who made the switch didn't know this, he or she may have neglected to completely flush the system of R-12 before introducing the R-134a. This would result in mixing the two, which can create a gelatinous substance and block the system. A blocked system can cause the compressor to fail.
2. Wrong conditions for optimal functioning
The refrigerant R-134a has different ideal functioning conditions from R-12. This means that in a system designed for R-12, it can have difficulty keeping up. This leads to an impression that it's a "less efficient" refrigerant, which is unfair. R-134a works better in systems designed for it than R-12 would, so naturally the reverse is also true. Additional conversion efforts may improve conditions; ask your mechanic for recommendations if you require a more efficient operation than you're getting from your retrofitted system.
3. System strain
The retrofit process can put more pressure on your air conditioning system, especially adding strain to the compressor. If your compressor fails and the system wasn't clogged, this could be the reason. In either case, though, the system will require a more thorough conversion (and repair). Your Mercedes repairman will be able to recommend appropriate system changes.
In some air conditioning systems, the R-134a refrigerant can simply escape through the walls. This is the case because it has smaller molecules than R-12 has, allowing it to sometimes pass through the sides of hoses, seals, and other components of the system. So if your retrofitted system isn't blowing cold air at all, the problem could simply be that the refrigerant has left your vehicle, not that it's unable to cool.
These four issues are common reasons for failure of systems that have had do-it-yourself retrofits performed. If one of them applies to your Mercedes, don't despair; your repairman will be able to recommend a conversion plan to increase the efficacy of your car's air conditioning. If you are looking for an auto shop with experience working on Mercedes cars, then try one like Benchmark Motors INC.