93 Astro AWD Not Working

I changed the transfer case fluid this fall when I bought this van and used Castrol Dexron 5 synthetic blend. Changing the oil really smoothed it out and I thought I was ready for snow. The old fluid was brown and smelled a little burnt but not to bad. We had our first snow this weekend and found out the awd is not working. I jacked up one side of the van ( in the garage after I got stuck in my driveway)and the front and rear wheel would spin but I could stop the front wheel from spinning with my hand and even turn it backwards. I changed the oil again and used the autotrac II but that did not make a difference. Any suggestions? How does the 93 transfer case work?
Thanks

What model transfer case? On the back side of the transfer case, directly opposite the front driveshaft, there is a tag that tells the model number. Are there any warning lights on? Are there switches to manually put it in, or lock it out of AWD? Does the ABS light work? Is the ABS light on while driving? Do the antilock brakes work?

I could not find a tag on it, only Borg Warner stamped on the case and number 13 72 065 901 stamped beside it.No warning lights are on, no switches to engage it. ABS is working and there is not an ABS light on. The light does come on though when I turn the key and goes of when it starts.