rear window vents not working...

I have a 98 Grand Caravan. Both of the side window vents near the rear of the van do not function. At first, it was just one side that would not work, but now neither side works. Is there anything I can check to possibly fix it myself? Thanks!

I had to same problem (kinda still do) with only 1 of the vents last year.. I got myself another motor from a local wrecking yard (which was tested and does work) and I still have a problem where it works when it wants too.. I suspect it's the actual switch in the driver door.. eventually I'll get around taking it apart to test it out.. I have a 96 Caravan