If the AC clutch is not cycling and the compressor is not turning, it’s likely low on refrigerant as suggested by B and C. First thing is to check if the system holds a charge, and that involves filling some refrigerant into the system and/or using gauges to see if it holds pressure. It’s not impossible for a Diy’r but you’ll need access to specialized tools and advanced mechanical knowledge when dealing with AC systems. I don’t know your skill level, but if you have any doubts or hesitation I’d suggest to take it to an AC shop and get it diagnosed. Aside from dangers of compressed refrigerant and oil, if you don’t understand AC systems you could inadvertently damage other parts, adding to your repair expenses. Of course there can be other causes, but refrigerant leaks are the most common. It takes a special sniffer tool or use of UV dye to isolate some leaks. Autozone will loan the tools if you leave a deposit for the full purchase price with them.
If the AC compressor is cycling properly and pressures are nominal, then it could be the air blend door under the dash that switches air paths or the heater control valve for the hot coolant. Most blend doors and heater control valves are are vacuum actuated, newer model blend motors may have electronics. One thing a Diy’r can do is inspect for vacuum leaks and disconnected lines. Any chance you just did some work on the van, like a stereo or something similar under the dash or in the engine bay where something might have knocked loose?