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-   -   Mist formation on the windshield with a/c on (https://www.team-bhp.com/forum/technical-stuff/154926-mist-formation-windshield-c.html)

I am posting this on behalf of my friend. The car in question is a 2012 Ford Fiesta Titanium TDCi.

The mist is formed on the inside of the front windshield after 10 to 20 minutes of AC usage in the car, its more prominent during the night. The windshield on the Fiesta is long and mist forms on the lower part first before spreading to the entire surface in sometime. Using wipers will result in faster mist formation and clouding of the complete windshield.

Here is a video of the same taken the other night. https://www.youtube.com/watch?v=rA5LfCmrJK8&

The 2011 Fiesta has a large vent on the top of dashboard underneath the windshield which normally blows hot air when the ACC mode is set to demister setting. We suspect the problem is due to some fault on this vent which always blows out air no matter what the blower setting is. When the demister is switched on, the same vent blows hot air and the misting disappears in about 20 seconds, but it again starts after 15 minutes when the demister is switched off. Its impossible to drive the car around with the demister switched on all the time.

The vent as seen through the windshield

The vent as seen from inside the car


What is Ford A.S.S is doing?
Took the car to service center close to five time, twice during the regular service and three times specifically to address this problem. Once, the car was left in the service center for close to a week for inspection after a complaint was raised to Ford. Every time, they just give the car back after a wash and the problem just doesn't go away. During one such service, they even left a dent on the left rear fender but that's not for this thread. :mad:

How is the car driven now?
Earlier, a sun shade used to be kept on top of the vent under the windshield. Not at all elegant but it slows down the mist formation considerably. After Ford tried to fix the issue, the misting became more prominent and the sun shade couldn't help. So, the vent was closed with a piece of plastic and some duct tapes. It helped until Ford removed them all when the car was finally taken to them for the fifth time.

Our not so elegant solution to the problem


What is Ford A.S.S is saying?
Ford claims its due to the following reasons.

1. Powerful AC :Frustrati
2. Common with all Fiestas, they checked three and all of them had this apparently. But I wonder how others manage to drive without complaining.
3. Very low temperature on ACC causing the mist, supposed to be driving around with 23 C as per Ford. Tried that too and mist formed still.

The help or the lack of it from Ford has been pathetic and no one with technical expertise or knowledge on the issue has been on the issue thus far. The lady from customer care calls back every now and then asking about the feedback on the service and its annoying. Unable to use the car at night due to this issue.

Has anyone with 2011/2014 Fiesta come across this? Is it really an issue with the blower and the vent atop the dash? Is the vent supposed to let out air only when the demister is on? Is it 'open' all the time on our Fiesta causing this issue? Any help will be much appreciated.

A common issue (wouldn't really call it a problem) with plenty of cars in very humid weather, not specific to the Ford Fiesta. Caused by leakage of cold air past the flaps inside the dashboard that regulate airflow to the different vents (face, feet, windscreen). Running the AC with a higher temperature setting (24*-25*C), or running the heater simultaneously, with the fan speed increased, will help to reduce the mist formation. Also, wiping the windscreen with a spectacle lens cleaner will prevent fog formation.

Don't think the ASS can really address the issue.

Agree 100%. In my Figo and Polo I keep the temperature very close to normal (between the blue and the red lines) and I don't face this problem. However, my Nano doesn't have temperature setting. The A/C on first setting causes this problem. Can't help it.

Our Swift has ACC and I keep either 24 or 25 C always. There is light misting on some days but very manageable. The formation on the Fiesta is really not comparable at all though. It appears and spreads at all temperatures unless the heater is on.

SST, could it be due to the leak being a little too high in this Fiesta?

I had this issue with my Ikon but that was after almost 7 years of use.

It was caused due to the sponge material inside those vents becoming brittle due to weather and age.
Dont know if they still use the sponge but could be helpful if the sponge is there.

All you need is to change the sponge and the misting will go.

Quite possible. In which case the airflow control unit will have to be removed and the foam air sealing material replaced (as arnabchak described) - which is likely to involve gas removal and recharging for the AC also.

Does Fiesta have outside temperature gauge? Set your ACC to match the outside temperature and your misting problem will go away.

Are you guys referring to the AC cabin filter?

That's not working either. :confused: It goes away only when the temp on the inside is higher than on outside.

No, there is a box-like contraption under the dashboard, which has flaps in it, which are moved either manually by a cable, or via a motor. That's what redirects the air in different directions. Not sure about the Fiesta, but in most other cars the box also houses the evaporator coil of the AC system.

No. Not referring to the AC filter. It is a layer of sponge materials places just below the air ducts on the top of the dash.

It is difficult to access but can be removed with wire and hooks.

Deetjohn, the problem is due to the Air Flow direction not working correctly and cold air being blown always . You have diagnosed it correctly.
Ask the A.S.S to sort this out.

Guess what. My friend checked an EcoSport and there is nothing coming out of the vent in other mode other than the demister setting. So, I guess we have found the issue.

Now, that's the tricky part. :) Is it a mechanical glitch (problem with vanes, flaps) or is a software glitch (the flap not getting the signal to shut when the mode is changed)?

Ford A.S.S rightly declined to cover the vent from inside saying condensation will create more problem with all the electronic bits sitting underneath the vent.

Hope the A.S.S guys have checked the sensor that sits near the duct(sunshine sensor?) and cabin thermistors.

These sensors could be working, but may not be providing right data. The ford system is heard to be fully digital and with digital sensor. It could be a single digital sensor going bad.(Info is from an "engineer" - with so much theoretical knowledge :D)