Air Condition is not working properly

first of all, the A/C isn't designed to be running well when sitting around. So, yes, it works well when going down the road as designed. For a car that old you might have some tubing that has holes in it or cool air is escaping elsewhere. Maybe you have a junction Y in your HVAC that is disconnected, or cracked in some fashion. If you don't know how to add freon you can have some issues applying yourself. Get' r in shop where it needs to be BUT why? it's already operating just fine going down the road.