So I was driving along with the air-conditioner on when I noticed what looked like smoke starting to come out the air vents. But according to the dashboard guage the car was not overheating and there was nothing coming from under the hood. On closer examination I don’t thing it was smoke but water vapor: it didn’t smell like smoke, dissipated into invisibility a few inches from the vent and I could see condensation forming on the windshield where the vapor hit, the amount of visible vapor varies when I adjust the temperature of the air-conditioner.
I am planning to consult a mechanic ASAP but until then anyone have an idea what could cause this?
The A/C condenses moisture from the air, which normally drips out through a drain tube. Sometimes the drain gets clogged and the water (condensate) pools up in the evaporator case, where it can slosh onto the floor and/or be picked up by the airflow through the vents.
Look under your dash for condensation on the outside of the airbox and also for water on the carpet. If it’s plugged up the condensed water has to go somewhere. Check to see if there is any water on the driveway after running the air conditioner.
I used to see this in cars on extremely humid days, and it was unrelated to any malfunction or plugged condensate drain. What happened (I think) was this:
Compressor runs, cools evaporator coil.
Evaporator coil cools air, cool air then cools downstream portion of duct.
Compressor cycles off.
Evaporator coil warms up due to passage of warm air.
Warm, humid air now reaches ice-cold duct walls downstream of coil.
Having only just now been cooled down past the ambient dewpoint, condensation (fog) forms in the air immediately before the air exits the duct into the cabin.
Normally when the compressor is running it cools the bajeezus out of the air, and then the downstream portion of duct actually warms the air back up just a bit before dumping it into the cabin, and you won’t see any fog. It’s only when cooling is the very last thing the air that you would see fog.
Other possibility: air coming from the ducts is so cold that it’s wringing humidity out of the warm, moist air in the cabin. Sort of the opposite of seeing your breath on a cold day, it’s just that instead of a warm humid jet of air into a cold environ, you’re dealing with a jet of cold air blowing into a warm humid environ.
That said, it’s still worth checking for a blocked condensate drain tube (see water on the ground under your car when you run the A/C while parked for a while? If not, that may be a sign of trouble), but if condensate is accumulating in your ductwork then another sign would be funky odors coming from the vents (due to bacteria/crud growing in the pools of condensate).
I have seen this quite often, in different vehicles, both here in OK and in TX as well. The hotter/more humid the interior the more likely to see it, IME. I guess its fairly similar to seeing the ‘fog’ roll out of a just-opened freezer door. On one particular car, the refrigerant gas was leaking slowly and each time my buddy recharged the system, he’d get very obvious ‘clouds’ just after the recharge (when first turning on A/C).
This doesn’t mean that something ain’t wrong with OP’s system, but it is not unusual to see those ‘clouds’ in certain climates.
Another possibility is excess moisture build-up on the evaporator fins. This could be caused by setting the A/C to maximum cold with low blower speed, which sometimes leads to ice build-up on the evaporator core. It’s best not to use the max cold/min blower combination.
I remember seeing an extra position for the A/C in my mom’s car in the Seventies that said “Desert Only”. What was that all about? Ice on the evaporator if used while not actually in a desert? Do modern cars just not have the extra “goes to eleven” studliness, or did they solve the problem?
I don’t know about all cars, but on some of them the “desert use only” position overrode the thermostat and made the compressor stay on all the time.
I imagine the reason those went away was that they designed better systems that didn’t need to override the thermostat to provide adequate cooling under harsh conditions.
Thanks all. It turned out to be a blocked drain. The car shop cleaned it out fo no charge. But since I was also getting the wheel bearings replaced which was not cheap, they could afford to not charge me for the air conditioning.