Minor water ingress into fresh air vent in driving rain

[Calikura]

As per title. By minor I mean on the order of a few tablespoons at most, coming from under the dash where the AC ducts are. Drip, drip, done. Carpets not soaked, no flooding.

Checked usual suspects:

• cowl drains (scuttle drains) are clear
• windshield seal (original, never replaced) passes the soapy water/compressed air test all around
• no moisture around firewall grommets
• AC condensate drain tube is clear
• dumped a few buckets of water all over the windshield and cowl area with the hood down while washing my car- completely dry inside
• door seals dry, rest of footwell completely dry except for the exact spots where the drops of water came down onto it

Am at a loss as to what else to check. It is a consistent problem now that the tropical monsoon season is in force. At its current scale it doesn't seem to be causing problems but I don't want it to get worse and cause electrical problems.

I've only had the car (a '08 Mazda2 hatch) for a year or so and I've only started noticing this happening and I'm wondering if it's just subpar design of the cowl area to handle extremely heavy rain, or if something is definitely broken that I need fixed..

 

[PimTac]

Did you drive through standing water?

 

[edwardh1]

wiper drive mechanism "holes" in firewall? my 60s and 70s chrysler products leaked there.

ask on a mazda forum- possibly a pattern failure others have too

 

[Calikura]

Originally Posted by PimTac
Did you drive through standing water?


Nope, I didn't. I'm also careful to park a little higher up on a hill in this season.


Originally Posted by edwardh1
wiper drive mechanism "holes" in firewall? my 60s and 70s chrysler products leaked there.

ask on a mazda forum- possibly a pattern failure others have too


Thanks, will investigate!

 

[PimTac]

If this just started then a good look around underneath is warranted. Sometimes the answer is not clear unless you visualize the process.

I've spent a bit of time in your region. On some cars during extra high humidity days the dash vents would spit water out. Some systems probably reach their limits.

 

[HoosierJeeper]

x2 on it being humidity. Used to be an every day thing when I lived in Florida...

 

[rekit]

I drove thru some deep water trying to get my wife to a doctor after Harvey flood. Turned around before it got too deep (Tacoma PreRunner) and never noticed any water. Truck sat parked for a few days, and 3rd day took a drive it and noticed a musty smell when I turned on the A/C. I believe water backed up the A/C drain in my case. I pushed some Hydrogen Peroxide back up it a few times and let it sit. Seemed to work better than Lysol sprayed into the fresh air intake up by the windshield while the fan was on high with Recirc off.

 

[Calikura]

Originally Posted by PimTac
If this just started then a good look around underneath is warranted. Sometimes the answer is not clear unless you visualize the process.
I've spent a bit of time in your region. On some cars during extra high humidity days the dash vents would spit water out. Some systems probably reach their limits.

It might be possible that it has been the way it is all along, but the extra heavy rains in recent weeks have made it more obvious to me. I've taken a look under the dash each time I get back to the car after it's sat in a heavy rain and can clearly see one or two drops about to fall from the downward-blowing AC vents or somewhere along the AC ducts.

Originally Posted by HoosierJeeper
x2 on it being humidity. Used to be an every day thing when I lived in Florida...

Does this only happen while driving with the AC on, or does it also happen after the car has sat parked under heavy rain (with extremely humid surroundings of course)? This has happened in my car several times in the latter case, which is puzzling. I can easily understand why it happens in the former case, but barring a leak or ingress through the fresh air vent (which I can't find evidence of in my car), I can't understand how it happens in the latter case.

 

[PimTac]

I may have misread the problem. It sounds like a very small leak from above. Windshield seal, cowl, windshield wipers.

It might be a very tiny hole and hard to discover.

Edit: to add, look higher up as well. Too and sides of windshield. Do you have a sunroof? Check there as well. Water can travel quite a ways before it shows itself as a leak.

 

[Calikura]

Originally Posted by PimTac
I may have misread the problem. It sounds like a very small leak from above. Windshield seal, cowl, windshield wipers.

It might be a very tiny hole and hard to discover.

Edit: to add, look higher up as well. Too and sides of windshield. Do you have a sunroof? Check there as well. Water can travel quite a ways before it shows itself as a leak.


After lengthy observations it turns out that you were absolutely right at the beginning. It was simply the inability of the car's AC system to cope with the incredible humidity (>99% RH) that lasted for days or weeks on end. After any length of AC use, drops of moisture would condense on the AC ductwork and parts of the (metallic) body panels adjacent to the ducts. If it was warm and dry while parked up, the moisture would of course evaporate and dry off by the time I got back. However, if it rained heavily in that time, the moisture would remain and proceed to drip onto my feet the next time I drove off. That was why I initially thought the culprit to be rainwater ingress.

To further back the hypothesis I used the AC on full cold for the entirety of an hour long drive, then ran a small battery-powered household dehumidifer behind the glovebox while the car was parked up under a raging thunderstorm all day. When I got back, the dehumidifier's reservoir was filled to the brim, while the ductwork was pretty much dry to the touch.

All this while the condensate drain was clear and there was no accumulation of condensate in the drip pan whatsoever. Refrigerant pressures are on the dot, the evaporator is clean, with no evidence of icing over.

Going to think about wrapping all the wiring under the dash in something splashproof..