I have a 2005 jimmy (blazer) 4.3L and within 5 min of starting the vehicle, I have been getting some sort of a light colored smoke coming out of my dash vents that clings to the inside of my windshield. There is a very faint odour to it (almost like burnt coolant) but then it stops after a couple of minutes and if I blow hot or cold air in full defrost mode, it seems to mostly disappear. I just had a coolant flush a couple of months ago but this just started happening 2 weeks ago.

 

You may want to check for a leaking heater core as this could be a cause. I would suggest using the search feature of this forum and you may see other posts that are similar to your issue.

 

I would say core as well. Check the floor near the transmission tunnel on the passenger side for wetness.

 

Leaking heater core for the win.

 

Yep! Guaranteed! Look through my album and posts, you will find all the answers, lol!