I have a 88 XJ Pioneer, 4.0, AW4, np231 and when I got it from my Dad's estate in 97 the part time light would not come on. I also did not hve working cruise control. I picked up a chilton manual then shortly later purchased all the manuals from Jeep.
I noticed vacuum leaks were listed in chilton for both systems not working. I went to my dealer and asked if there is a vacuum harness for the 4x4 system for the shift motor on the axle. The guy pulls out the part and I pay him for it. I am totally new to XJs and spend a week trying to figure out where this stupid hose goes. I finally found it, it connect to the shift motor which is directly under the oil filter then up to some metal tubes.
If you have the NP231 transfer case (part time) then go buy a new shift motor harness at the dealer, they runa bout $10.
If this is an older XJ then change the CCV system harness under the hood. There are 3 assemblies you buy at the dealer. This will give you new vacuum lines for the fuel pressure regulator, EGR valve everything else that hooks up to the intake manifold. Here an article so you can read up on the system. If you also have oil in the air box chaning the tube at the back of the valve cover will fix that problem.
http://www.off-road.com/jeep/cherokee/xjtech/engine/40ltr/blowby.htm
Also pick up a new oil filler cap, they run around $3 at the dealer or your local parts store. Stant makes that butterscotch colored cap.
In 97 I replaced all those components and if make my XJ run better. They fixed my 4x4 problem, and solved all my vacuum leaks. The items in the link I gave are 50,000 mile replacement items so you are not doing anything unusual.
Like Eagle said check the vacuum lines around the battery, lots of people have problems with the acid doing them in.
If your blower motor is working and you need to look at vacuum. I understand if there is a vacuum leak the vents go to defrost, do you get air out of the defrost vents?
Also do you get the different speeds out of the fan? There is a resister assy which is used to adjust fan speed. That component could of failed.
I can explain more on any of these if you want, let me know.