White smoke coming out of vents

Question

Yesterday I was driving my 97 Accord down the highway with the air conditioning turned on.  It started raining heavily for a little over 5 minutes, and then the rain stopped.  Suddenly, what appeared to be whitish smoke started coming out of the 2 center vents.  I quickly turned off the air conditioning, and the smoke stopped coming out.  After around 10 seconds, I turned the air conditioning back on and no smoke came out.  I drove for another 30 minutes and didn't see any smoke again.

I have never seen this happen in any car in my life, prior to yesterday.  Also, it may not have been smoke, because I did not smell anything - so maybe it was water vapor?  None of the warning lights on the dashboard lit up.  Also, I had the ventilation system set to "recirculate" and was not using the defroster.  Any idea what might have happened?

Edit: On 2 occasions in the past week, on sunny days, I have seen similar white smoke with no odor (although not quite as thick as what I described originally) coming out of the vents for about 10-15 seconds with the AC turned on.

fred_dot_u · Answer

You did not indicate any foul smell, which eliminates a coolant leak, as the odor would be obvious. I believe the key factor is that you've described a heavy rain. If your ventilation system was set to allow outside air, rather than recirculation, it's likely that some of the high humidity (heavy rain) was pulled into the ventilation system.

It would have been sufficiently heavy volume to condense from the cooling of the air conditioning system and present itself as your own personal cloud.

I have experienced this effect in the same conditions as you describe. To prevent it in the future, when you encounter heavy rain, switch to recirculated air until you exit the area, or you can choose to ignore or revel in your temporary cloud with a silver lining (no troubles).

user38183 · Answer

I had a similar issue happen to me, it wasn't raining though and it wasn't on the highway

I was driving back from my uncles house that's about 20 miles out of town, once I got in town I stopped at the first red light and all of a sudden, white smoke started pouring out of the vents, I immediately turned off the road, popped my hood and stepped out and white smoke was pouring out of the cabin, I waited a few minutes after checking everything and then started it back up, everything was fine, all until I got home. It started up again

I took it to the Mechanic the next day thinking "oh no, what's this going to cost for a new heater core" he had it for 5 minutes and fixed the issue

It was the coolant resovoir cap, one the seal was bad, and two the threads were stripped. New tank, new cap. Never happened again.

I'll tell you what though that sudden dense white smoke filling the cabin about makes your heart drop.

White smoke coming out of vents

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