AC works best when sitting still.

So they didn't flush the system, that was needed to happen. You may find that it is charged properly and it will still not function right, because there is a crap in the system. Most shops, especially with warranty work, they just get it in and out the door as fast as possible.

 

Check those valves , if they closed ac works great , if open - likewarm ....had exactly same symptoms

 

The fan won't cycle at all while driving. At least it shouldn't. It works like the radiator. Enough air flow that it's not needed.

Even cars aren't using the fan anymore unless it's sitting.

 

I had this same exact problem on 3 different trucks. Each time the part they replaced to fix it was called an actuator.