What is happening if there is smoke coming from the ac vents in the dashboard, but don't have a smell. It happens once the car has been running and after it rains, it sounds like water is sloshing around the ride side of the dash. hat is that?


Asked by Jul 21, 2016 at 02:55 AM about the 1999 Mercury Grand Marquis 4 Dr GS Sedan

Question type: Maintenance & Repair

3 Answers


Sounds like either a plugged condensation drain in the heater core plenum box or a leak from the window cowl. It isn't smoke but vapor/steam. Water, either from a leaky cowl or from running the AC, is building up in the plenum box and simply can't drain or drain fast enough to keep from sloshing around against the heater core (which is always hot) and turning into steam/vapor. Running the AC might cause this too. Find the end of the drain tube and fish a wire up it to clean it out.

Tom Demyan

Probably a leaky heater core. Is there a film on the inside of the windshield?


Thanks guys. It was a leaky heater core.

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