If, you have a roof mounted A/C unit on the rear. Then, you may have to change the expansion valve.
General A/C not getting cool:
1. Expansion valves may be plugged, overtime, they may become oversized and not cool properly. Think of a ball point pin with little tiny holes. That's your expansion valve.
2. The Dryer on a car is suppose to remove moisture in the A/C system. Over time this gets full. Water particles are in your line causing the expansion valve to prematurely freeze. Causing the A/C system not to function properly.
Expansion Valve & Dryer are cheap for the Durangos. I purchase mine from an A/C supplier shop locally here in Phoenix, Az. If, you go to the dealer, they are way more expensive. There were 2 o-rings I had to goto the dealer for because, the o-ring kit wasn't big enough. Expansion Valve around $25, Dryer was around $15, o-ring kit around $5
If, you have a compressor, you can goto harbor freight to get a vaccum pump for $12.99.
Get you a set of gauges: $29
Set your compressor to regulate at 90psi for the vaccum portion of the Job.
Once, your system is vaccummed. Charge the low side with the can turned upside down. Since it is liquid.
Your high side pressure should be 2X or 2.5X the outside temp.
Example. If your outside temps are 100deg, your highside pressure should be 200-250psi @ 2000 Engine RPM.