air conditioning questions?

two questions can you put 134r in a system that is a r12 system to top it off. i am getting some cold air and was wondering do i have to take the r12 out first or can i just add 134r on top off the r12. part two where is the low side fitting for ac on a 89 grand prix with a 2.8 liter engine. any help would be appeciated thanks all you rock.

i have heard mixed reports about mixing....for this repair i think its best to have a shop do the work...most shops have the machine to evacuate the old freon....if you try to drain the r12 by hand most will come out but....its against the law...and is not good for the OZONE...also doing it this way will not completely purge the system of old r12, therefor you will be mixing the r134 anyway

when you go to auto store ask for the retro-fit kit to do this...there should be instructions how to do this...

DO NOT mix refrigerants. You need to take the car and have it evac'd and converted. The different refrigerants require that all the old oil be removed as well and flushed and the correct oil put in. If your air is still somewhat cold, I would suggest depending on the laws in your state taking it to an a/c shop and just getting it topped off with r12. A proper conversion with a full flush will probably cost you more than the car is worth. R12 is still available in a lot of areas, just expensive. But still cheaper than converting if all you need is topped off. R12 cools better than 134 in the old systems anyway.