Sounds like it froze up with the lack of air flow. Do u run it in dusty environments? Down here in clay country, trucks on construction sites and rock quarries would clog up the evaporator. It is usually in place where a lot of earth is being moved.We would remove the blower motor and reach up into hole and blow out the evaporator with regulated air psi before the a/c was turned on. You could see it though. Some looked to have been stucco'ed.

I looked at the breakdown for 2011 and it looks like you can do that. I was surprised they did not put a cabin air filter in it as it seems ford is putting in everything else. The other thing we have had a problem with on the 08 and newer trucks is the space between the radiator and condenser filling with debris.

If neither of those are the problem, then it would take psis to see what it is doing. Could be anything. Is it dual zone auto climate control?

I know times are tough but I think I would ask to speak to Ford rep if it comes that to see if they will cover with that age and mileage. We have had limited success depending on the issue.