Smoke out dash vent with AC on
 

2000 Accord 4cyl. 150k miles

My daughter is on a road trip and called me yesterday on the road. She started getting smoke from her dash vents only when the AC is on. It goes away when she turns the AC off. She said it hadn't been cooling as well for a couple days and thought it might also be a little noisier.

She's at my sister's place now and my brother in law is looking at it. He can't find anything unusual although he says it seems like it should be cooler.

I searched the subject and read some earlier posts on this subject but didn't find any that really matched her conditions or any that had any resolution.

Any ideas what might be causing this. She said it kind of smelled like burnt rubber. My bro in law said all the belts look perfect.

There are only two kinds of smoke that can come out of the vents on an a/c system. Water vapor or Freon. Does she get "smoke" immediately after turning on the a/c? Water vapor will have a slight smell, but R-134a will have a stronger chemical smell.

I will talk to her more about it on Monday. She had been driving for a couple hours in 100+ heat on the interstate when it began. It stops when she turns off the AC. I'll check if she also turned the fan off.

What condition would create water vapor? She was driving in a hot dry environment.

Normally that happens in a hot HUMID environment. The AC is condensing water from the humid air.

I've observed smoke from the AC vents only once - in my son's '86 Prelude. 'White' smoke, no particular odor.
I immediately guessed it was a freon leak (in the evaporator ?) which would cool the air super cold -
freon cools when it expands; so it was condensing water in the flowing air stream. Dry climate - 9" rain/yr.

Sure enough, the AC unit never cooled after that although the fan blew.
Didn't repair the AC, drove car to the ground.

Agreed... It's the same thing as when you exhale outside in the cool weather. If the A/C is still functioning, it's not refrigerant, there isn't much in there really.

If this is troublesome to your daughter, the effect is lessened if you turn on "recirculate". Then the air being drawn into the system is from inside, and normally carries less moisture as the interior cools down.

Tell her it's the same thing as the "fog" seems to come off a bowl of ice cream. Doesn't prevent people from eating ice cream when it's hot & humid outside...

If it were actually leaking refrigerant, that leak would not stop when you switch off the AC. It wouldn't stop leaking until all the refrigerant is gone, then the AC wouldn't cool any more.

Re-reading the first post, I have another thought.

When the refrigerant is low, the system operates at a lower temperature. But even tho the temperature is lower, it has LESS cooling power. That could be a very slow leak that took a year to get to this point.

The way to fix THAT problem is to have an AC shop measure high & low -side pressures & add refrigerant if needed. Possibly add dye to the refrigerant so they can see where it's leaking.

OK I got more information now that she's home. She said it kind of smelled like burnt rubber. Very faint though. The AC is working most of the time but sometimes it blows warm air then it will work again the next time she starts it. She hasn't had anymore of the smoke/vapor since that first time.