S Type front window misting at start up

[John D9395]

Hi

This mainly happens after I have run the car, stopped for a while, and then get back in to continue my journey, in that when I re-start the engine, the fan / vents seems to blow out warm / moist air up the windscreen and front side windows causing them to mist up.

I have had a new wiundscreen fitted recently, and whilst the guy had it all in bits, I checked around the pollen filter, and it all seemed as dry as a bone.

I am guessing that there is water sat in the vent system somewhere, but where?

Any help appreciated

[V88Dicky]

I've seen this on most cars, when the aircon / climate has recently been switched off. Do you have it on constantly, or only run it when required?

[John D9395]

Hi

I always leave it totally on 'auto', ie A/C always available if the system requires it

[fatboy b]

John D9395 said:

Hi

I always leave it totally on 'auto', ie A/C always available if the system requires it

My 14 month old XF does it in damp weather. Soon clears once the aircon kicks in.

[John D9395]

Mine clears fairly quickly, but why does it happen?

I had a Citroen C5 years ago, and one of the sales features was that the fans always blew air into the foot well on start up to clear the system of any damp air before blowing air on the windows.

This is my 2nd S Type, and I don't remember it happening with the last one, which is why I am thinking there is a problem that might be able to be fixed.

Surprised it happens on a 14 month old XF!

[anonymous-user]

John D9395 said:

Mine clears fairly quickly, but why does it happen?

I had a Citroen C5 years ago, and one of the sales features was that the fans always blew air into the foot well on start up to clear the system of any damp air before blowing air on the windows.

This is my 2nd S Type, and I don't remember it happening with the last one, which is why I am thinking there is a problem that might be able to be fixed.

Surprised it happens on a 14 month old XF!

If it's misting, there must be moisture in there. Carpets dry? Any leaks?

[John D9395]

Car garaged every night, all carpets, boots etc dry as a bone, hence my thought that moisture is sat somewhere in the air duck's, but where? Is there a known problem area or a blocked drain hose?

[SV8Predator]

John D9395 said:

hence my thought that moisture is sat somewhere in the air duck's,

I sympathise, the problems can drive you quackers.

I've seen the problem before, in a non-AC car there was never any problem.

But in an AC car the problem was as you described.

Never solved it (sorry) but put it down to moisture condensing on the AC evaporator (under the dash, part of the HVAC unit) and remaining after everything was switched off. Next morning, (or whenever) this moisture is blown up onto the screen, but once the AC kicks in (and thus removes moisture) it all clears.

Didn't happen on non-AC cars as they didn't have the evaporator (holding moisture) next to the heater matrix in the HVAC unit.

[fatboy b]

REALIST123 said:

If it's misting, there must be moisture in there. Carpets dry? Any leaks?

Could be on the carpet mats as a result of the current weather - in and out the car with wet shoes. A few short journeys would see the moisture build up a little.

[John D9395]

Carpets and mats dry, moisture / dampness is coming out of the vents.

As per earlier post, car is garaged every night, and I don't tend to park in or next to puddles, as I like dry shoes as much as a dry car

[anonymous-user]

This is very common with cars with AC. After the car is switched off the ice and moisture condenses off the evaporator (thing that cools the air). All the air passes through this evaporator and is then heated back up as required, so when the blowers come on first thing they pick up this old moisture from the evaporator. A better design for draining the evaporator might help, I did find the S-Type was particularly prone to this. Guess it's yet another half arsed bit of design on Jaguar's part.

[SV8Predator]

dme123 said:

This is very common with cars with AC. After the car is switched off the ice and moisture condenses off the evaporator (thing that cools the air). All the air passes through this evaporator and is then heated back up as required, so when the blowers come on first thing they pick up this old moisture from the evaporator. A better design for draining the evaporator might help, I did find the S-Type was particularly prone to this. Guess it's yet another half arsed bit of design on Jaguar's part.

Good post! I wish I'd thought of that.

[Jaguar steve]

SV8Predator said:

dme123 said:

This is very common with cars with AC. After the car is switched off the ice and moisture condenses off the evaporator (thing that cools the air). All the air passes through this evaporator and is then heated back up as required, so when the blowers come on first thing they pick up this old moisture from the evaporator. A better design for draining the evaporator might help, I did find the S-Type was particularly prone to this. Guess it's yet another half arsed bit of design on Jaguar's part.

Good post! I wish I'd thought of that.

The solution is to run the system at full heat with the a/c off for a few minutes at the end of your journey. That allows the residual frost on the evaporator to melt and drives all the resultant moisture from the system so it's left dry. Regularly removing the moisture also prevents the growth of bacteria in the system that's the main cause of contaminated a/c systems smelling like wet dogs.

[John D9395]

That's good advice, next time I am out in the car I will do the whole journey with AC off and report back.

Thanks for advice