My air conditioning only blows thru the defroster and floor vents. It alternates between the 2 under load while driving. It comes out the top while accelerating and the bottom when going and no loads for acceleration. The rear air does not blow cold at all. What could be the issue? I do get some cold air but in a full size conversion it needs to work. it has the 5.2 engine and the year is 1999 ram 1500.

 

The problem with the front is either a vacuum leak or a bad check (one-way) valve in the vacuum line.

If the front air is cold but the back isn't, then I'd say your freon charge is okay and the issue is likely with the rear blend door not moving all the way over. If it's allowing heat to pass, then even if the air starts cold, it's being warmed up before you get to feel it.

 

Not knowing what year your Ram Van is, it's hard to say where the vacuum issue is. In general, there have been three HVAC systems for these vans from 1971 to 2003.

As for the rear AC not working, there is a valve in the coolant line that needs to open to circulate to the back. I can't recall what the term is for it. Or, like Alloro stated, the vacuum actuation may have failed or gotten stuck (older models) or the Yellow "C" actuator made by CEI (Saia-Burgess) has failed and needs replacement.

My CEI actuator is still on my rear unit. I had unplugged it to allow the baffle door to blend air to both the feet and over head vents. It's dumb not to blend for back there. Either the feet freeze and the head heats vise-versa.