I assume that this is related to the vacuum pump. Anything in particular to look for ? Sometimes the dash selector will work fine for heat, defrost, etc. I have never had it engage the hubs, but only tried 1 time. The 4wd does work with the hubs manually engaged. The hubs do have what looks like a vacuum line coming out fo them, along with the ABS line.

thanks

 

If it defaults to defrost then you have a vac leak. Start at the lines going to the hubs and work back to the pump.