I use R134a in my 90 GL.  It seems not as cool as "normal". The site glass
shows lots of little bubbles passing by - so many that it looks almost, but
not quite, frothy. I guess that means I am a little low.  I don't have a
guage and don't know much about AC.  Should I just add R134 until the
bubbles go away? Or is that too unscientific?