Auto Air Conditioning & Heater Repair: AC Low presure valve (where is it?), presure valve, freon

Question
Hi I have a 99 expedition EB 2wd.  I want to recharge my ac but dont know where the low presure valve is.  I see there is one near the radiator on the passenger side, with a black cap sticking out.  Is that it?. Lastly which can do I  do I use, a refregerent or the one that says add oil to your AC.  Umm,  please be specific to where it is.  I do not know anything about cars

Thank you

Answer
Adding freon without having the proper gages to put on the system of which tells you exactly how much freon to add to the system can be vary dangerous as you can damage the ac system if you add to much freon.

Have a professional ac shop perform this task as I would not want to see you get injured by putting to much freon in the system so as a hose EXPLODES as the freon is very dangerous is gotten on your skin and or you damage the system by adding to much freon.