Well the vents are fed by tubes so probably not wiring/electrical smoke, it couldn't get into the tubes.
And how long does the vapor come out of the vents, and how long does the truck have to sit before vapor comes back?
You are in Calif. and the sun does heat up the dash even on cooler days.
I would check that the evaporator tray drain hose is open, not clogged up, it comes out under the passenger floor pan near the center hump, push a wire up thru it, it is just a rubber hose open at the top.
It is just water in the evaporator tray so it wouldn't have a smell, like coolant would(leaking heater core).
After truck sits a bit, do not start it or even put the keys in it, but blow thru the center or passenger side vent and see if the vapor comes out drivers side.
If it does then for sure not an electrical issue.
Last edited by RonD; 04-12-2016 at 12:15 PM.