Does any one know what refrigerant was used on my 1991 190E 2.6? The compressor and aux fans have stopped coming on and I want to add refrigerant. Should I hot wire the low pressure switch first to check on compressor and fans? Thanks in advance for your help.

Your car originally came with R-12. Unless it was converted to 134-A recently you should still have R-12. Unless you have a set of A/C gauges I don't recommend this as a DIY job.

I agree with chowpit, ...have the system check by an A/c tech. There could be more discrepancies in there that you may not expect. Also, ..it would be better if you request to have the system retrofit for R-134A and use copper evaporator. It will pay off in the long run.