'99 T&C... during the summer I turned on the rear blower for the air conditioning once and when I parked there was smoke (not steam) coming from the driver's side rear wheel well. I've used both the a/c and heat with only the front blower on since then with no problem. I rarely drive the van but I might have to start using it regularly soon so I'd like to see what I can do about this problem. Any advice is greatly appreciated.

 

As the rear heat/a/c and blower is a self contained unit. Remove the Interior trim panel on that side and INVESTIGATE. The blower motor may have bitten the dust, but you will definitely know once you can see the whole unit. But where are you located, as ALL rear units I have seen and driven the unit is in the Passenger (Right Rear) rear corner.

 

Thinking about it now I think it was the passenger side... I've found a couple videos showing access so I will look into it once the weather warms up. Do you know how difficult it is to actually replace the blower motor? I'm not a mechanic but I can do repairs that aren't extremely complex. Would the Haynes book help with this?

 

While it is not near as good as a factory service manual(for all you purists),It does give good basic instructions for most common things the average DIYer can do..So yes, it would be helpful.
Biggest job is to remove the interior trim panel for access, from there it is simple couple of bolts to remove the blower motor and fan. A replacement most likely will come with new "squirrel cage" fan.
Once you get the trim panel off you will be more than able to see what is going on and what it will take to repair it.