[DeTomaso] use sight glass in AC that has been retrofitted to 134a?

After switching the AC system to 134a, do you use the sight glass in the dryer or go by the pressure at the low pressure port like with modern cars? Sorry, but I don't recall what I learned several years ago when I switched the system over. Jim Oddie After switching the AC system to 134a, do you use the sight glass in the dryer or go by the pressure at the low pressure port like with modern cars? Sorry, but I don't recall what I learned several years ago when I switched the system over. Jim Oddie