I have a 2012 Fiesta SES and my AC has been acting up for a few years now but I think this summer will be too hot to suffer through another year. I want to say about 3 years ago I very stupidly put about 4 cans of stop leak and refrigerant in my car over the course of one summer. It still works sometimes but only if it is less than 80°F (27°C) and/or if the sun is down. It also works best if my car is going in between 40mph and 60mph (64kph and 96kph) and on top of that, the fan only blows out any kind of air when the speed is on a 3 or 4, not on 1 or 2. It has been looked at by a mechanic and I was told that the whole system needs to be replaced but they were doing an overall check on my car, not particularly looking at that one area and that car shop (family friends of my step dad) run a European Classic Car shop, which a Ford is neither.  I have already put more money into this thing than I would like to admit and don't even know where to start when it comes to identifying and hopefully fixing the problem. Thanks in advance! 

That much leak stop has probably found it's way into components that it shouldn't have done and gummed them up.  Can't really be 'cleaned' out...so the best option would be complete replacement of all components in the system.  Not worth the cost.  Might be better off changing car instead.