I have a 2010 I bought used a few years ago. The ac has always been disappointing compared to my 07 1/2 ton but it only seems to get worse the blower motor works and changes speed when you change the setting. I took the blower motor out I made sure the recirculate door was operating properly and not broke. I know that the 3rd gens had a lot of issues with the outside air/ recirculate door not working properly is that a problem on the 4th gen too. I am out of ideas and this is my family vehicle and the wife and kiddo don't do so well in the hot car. Any suggestions on what could be wrong.

 

Welcome to the site, first check to see if someone has installed a cabin air filter, if so it's plugged by now, here is a link for the cabin air filter. https://www.dieseltruckresource.com/...d-t284729.html If no cabin air filter the evaporator core could be very dirty. Next try to turn the fan squirrel cage by hand it should be free to turn if not it needs a new fan motor, the bearings can get tight when hot and there is no way to fix. If it blows the same in both AC and Recirc then the HVAC intake is not plugged outside. One other remotely possible thing is the evaporator core is freezing up or the plenum is part full of water.

 

There is not a filter installed. The blower moves freely and I know it works I pulled it out and turned it on and it was able to spin very fast. It blows nearly the same on both recirculate or outside air. Is there any easy way to check for the other items you mentioned. I have no knowledge of ac systems.

 

I would next check to see if the evaporator drain is open, the drain is a small pipe about the size of a finger that comes out from the firewall down low on the passenger side, I would try gently poking something in there but be careful not to damage the evaporator core. If it's humid outside and there is a good amount of water in there it's possible to see condensation on the outside of the plenum under the dash with the AC running and will show the water line inside. Baby mice can find their way in then be unable to get out clogging the drain.