r-134 converted 190 16 valve.

I have a 1986 190e 2.3-16 valve that has been converted to r-134 refrigerant. I followed the 80% rule in refilling the capacity aand found that this does not work. All cars are different in how they react to the refilling. I had the shop refill the car to 1.8 lbs, 80% of the original r-12 2.2 lbs specs. The low pressure switch blew and the car never really got cold enough when the temps hit 90 plus. Upon replacing the low pressure switch, I asked the shop to refill the 134 refrigerant to 1 lb( 16 oz). The car can keep up with the weather now. I think that the car was filled to much using the 80%rule. I suggest to all r134 conversions to try filling to 50% of capacity and see how the a/c handles in the heat. Thanks, Joe