On the 2500, I have narrowed down the A/C cooling problem. Temp out of the condenser is too hot. If I put my shop fan in front of the truck the A/C cools great. Temp out of the condenser is so cool you can hold on to it.
Now, is the condenser fouled or is the mechanical fan not working correctly?
The fan turns, put how fast should it be moving. Diesel rpm's are low at idle.
I did find a black powderish stuff on the outlet of the condenser.