This is an 03 2500. I will get on the highway and on a hot day 80+ the ac blows great for a half hour or so and then slowly stops blowing but still sounds like it's blowing. Cold air is still coming out just at a trickle. I looked this morning and there's a metal tubing line that is getting frosted up. I'm not thinking its a door issue since the heater never has any issues. Maybe I'm wrong. I attached a picture and am pointing to the line that's freezing. Thanks

 

The picture looks like it is the low pressure line that is freezing. Hook up some gauges and check to see what the high and low side readings are.
Also check for mouse nest they love getting up in duct work if they can.
The air flow issue can cause the evaporator to freeze and the low side line.

 

Update looked at blower motor to find the connection was hot and plastic had melted. Recirc door does not fully close.

 

Cool nice find my fan switch started acting up recently sometimes I have to turn the switch on and off a few times.

 

yeah, so I am thinking that since the fan was not moving the air that's why the line was freezing up. we will see what happens.