Can Outside Humidity Affect Vapour Coming from AC Vents in a Car?

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Discussion Overview

The discussion revolves around the phenomenon of visible vapour coming from the AC vents of cars, particularly in relation to outside humidity and internal temperatures. Participants explore whether this occurrence is normal and what conditions may contribute to it.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions if there are normal circumstances under which vapour can be seen from AC vents, suggesting a connection to outside humidity and internal temperature settings.
  • Another participant shares a personal experience of their AC malfunctioning, indicating that visible vapour may be a sign of a problem, referencing a past incident with their vehicle.
  • A different participant confirms having experienced visible vapour from their AC vents, implying that weather conditions likely influenced this occurrence.
  • One participant proposes that the vapour may result from cold air from the vents interacting with warm, humid air inside the car, leading to condensation.
  • A participant provides a technical explanation, stating that the AC chills warm, humid air, causing the relative humidity to exceed 100%, resulting in fog formation that exits through the vents.
  • Another participant expresses concern about a potential leak in their AC system, indicating anxiety over the reliability of their vehicle's air conditioning.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the vapour is a normal occurrence or indicative of a problem. Multiple competing views remain regarding the causes and implications of the vapour seen from AC vents.

Contextual Notes

Some participants reference personal experiences and anecdotal evidence, which may not fully account for all variables affecting AC performance. There is also mention of a potential leak, which introduces uncertainty about the reliability of the AC system discussed.

Who May Find This Useful

Individuals experiencing similar issues with their vehicle's AC system, those interested in automotive maintenance, or anyone curious about the effects of humidity on air conditioning performance may find this discussion relevant.

DaveC426913
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Are there any normal* circumstances under which one might see vapour coming from the AC vents of one's car?

*non-broken-thing


I'm wondering if it had something to do with the outside humidity and the internal temp or something. It was about 28C out, and it's a sunny, muggy day. I had the internal temp at 22. It seemed to happen only when the car was in motion; the moment I pulled over it seemed to stop but if I started back on the road, it would start up again.



On the other hand, when I shut off the car today, the AC made that long, rattly, breathy sigh before going quiet. Has my AC finally given up the ghost?
 
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Oh, my AC on my old SAAB 9000 Turbo did that right before it started spitting little chunks of ice at me. $600 later I pick it back up from the repair shop and about 5 minutes from the place it starts spitting out little ice pellets and dies. I drove it back to the shop, "OH, well, what we did needing fixing, but there must be another problem." Quote to fix 2nd problem $700, because they have to take everything apart again. I told them where they could stick their quote.
 
DaveC426913 said:
Are there any normal* circumstances under which one might see vapour coming from the AC vents of one's car?

*non-broken-thing

Yes, I experienced visible vapour (misty haze) coming from my air vents just a couple months ago. I have an 04 Accord with no problems. I don't remember the circumstances though, but I'm sure weather conditions played a part.
 
It might not be mist coming out of the vent so much as the cold air from the vents forming mist when it hits the warm wet air inside the car?
 
Evo said:
...

(giggle giggle)
 
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It's completely normal. The AC takes in warm, humid air from outside and chills it. The relative humidity goes up as the air is chilled, and goes over 100%. The water condenses into a fog, and comes out the vent.

- Warren
 
K, thanks. I'm a bit paranoid because I know there is - or was - a tiny leak. It drained once but when I had it repaired they found nothing. I'm driving on eggshells, waiting for it to go kerflooey.