changing value in coolent side of air con whitch valule do I use

You don't use anything unless you are certified by the Environmental Protection Agency (EPA) to be compliant with Section 609 requirements for refrigerant handling. If you don't know where to put it, you shouldn't touch it. I'm all about "do it yourself" work, but when you're dealing with refrigerants, leave that to the professionals. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops