Air conditioning

I have a 92 dakota with out air conditioning. I got a r134a system from a 95 dodge dakota. There seems to be a pressure switch on the high side line of the r-134a system that on the r-12 system there is not one. Can I wire in the high side pressure switch in to the r-12 system?The r-12 system has a pressure switch on the low side and one on the expansion valve. On the r-134a system there is a pressure switch on the accumulator and one on the side side line.