Front window demisting issues (cold weather)

[moonigan]

I'm in an ongoing debate with my dealer about my cars sudden inability to demist the front window first thing in the morning when its cold even after the engine has been running for 30 minutes and would like to hear if other B8 RS4 owners have similar problems.

I'm now into my third year of ownership and for the past two winters my routine when the windows are frozen over has been the same.
Start the car, front demister on, temp set to hi, rear demister on. I then go and get a brew and wait for the kids and within 15 minutes the car is getting toasty and the windscreen has started to clear.

However this routine no long works as the car refuses to start blowing hot air through the vents until the car starts moving. Doesn't matter how long the car is sat there at idle (30 mins is longest so far) it just refuses to demist so I have to resort to wiping the inside of the windows with a cloth so I can get off my drive. Within 100M of driving the car starts pumping hot air into the cabin, its as if a flap opens that suddenly allows this to happen.

I've spoken to Audi who have had the car in and they say everything is working OK and suggested I needed to change the process I used so rather than putting the front demister on immediately I should allow the car to warm up and then but the blowers on but this still doesn't work.

I've fired off a few e-mails but I suspect they are burying their heads in the sand and ignoring the issue. Before I start to escalate this I'd be grateful if you would let me know if your car does the same.

Cheers
Paul

[DeanoC]

It is weird that it has changed. Mine was terrible but like any car it depends on what is on the glass and how you shut it down.

I cleaned the glass with IPA and the used fog-x and make sure i close it down on recirculate to keep the moisture out and it is a 2 min affair now.

Mine does blow hot air on the screen before i move

[Rw@@dy]

Does the outside temperature reading look ok? Mine sometimes goes mad and this affects how the heating/cooling works. This on a b7 by the way

[geoffdunk]

I have no issues although my routine is not quite the same. Climate set to auto as it ALWAYS, front demister on and rear demister on, that's it, no need to set temp to high as AC de-humidifies the air helping clear the screen even with ambient temperatures. Front demister on fires up once the temperature sin the system allow it, its a cleverish system.

You will notice the fans don't ramp up straight away.

DO you have your AC on all year round or only when you want cold air? Mine never gets switched of an never leaves the auto setting, 22 degress and set to AUTO 365 days a year unless I need a colder temp during the summer and i drop it to 19 and a really hot day but never turn AC off and always leave it in AUTO.

[geoffdunk]

It is weird that it has changed. Mine was terrible but like any car it depends on what is on the glass and how you shut it down.

I cleaned the glass with IPA and the used fog-x and make sure i close it down on recirculate to keep the moisture out and it is a 2 min affair now.

Mine does blow hot air on the screen before i move

There is no need to put the system into recirculate before shutting down, the system closes of outside air automatically, most modern vehicles do especially the better designed ones like the German marques. Modern HVAC systems are pretty clever and have automated startup and shutdown sequences programmed in.

[geoffdunk]

Also, do you have anything on the top of the dash covering the sun sensor, this will have a big impact on the HVAC system both at cold start and normal operation.

[DeanoC]

It is weird that it has changed. Mine was terrible but like any car it depends on what is on the glass and how you shut it down.

I cleaned the glass with IPA and the used fog-x and make sure i close it down on recirculate to keep the moisture out and it is a 2 min affair now.

Mine does blow hot air on the screen before i move

There is no need to put the system into recirculate before shutting down, the system closes of outside air automatically, most modern vehicles do especially the better designed ones like the German marques. Modern HVAC systems are pretty clever and have automated startup and shutdown sequences programmed in.

Oh really. It's been habit. Nice one.

[geoffdunk]

Audi have had cabin seal function since the B6 A4, my old S4 used to run through cycles at startup and shutdown, the B8 is a bit quieter about it but it still happens.

But with AC, or in this case climate control on the humidity is quickly drawn from the air anyway as this is part of the process and why you get that trickle of water on your drive in hot weather sometimes.

[moonigan]

Does the outside temperature reading look ok? Mine sometimes goes mad and this affects how the heating/cooling works. This on a b7 by the way

Yep. Outside temp looks OK. I did a video for Audi so they could see it and the car gets colder on the inside but they are still saying its normal because the computer diagnostics didn't return any errors.

Here's the video: https://www.youtube.com/watch?v=BoFomg6sRlA

[moonigan]

I have no issues although my routine is not quite the same. Climate set to auto as it ALWAYS, front demister on and rear demister on, that's it, no need to set temp to high as AC de-humidifies the air helping clear the screen even with ambient temperatures. Front demister on fires up once the temperature sin the system allow it, its a cleverish system.

You will notice the fans don't ramp up straight away.

DO you have your AC on all year round or only when you want cold air? Mine never gets switched of an never leaves the auto setting, 22 degress and set to AUTO 365 days a year unless I need a colder temp during the summer and i drop it to 19 and a really hot day but never turn AC off and always leave it in AUTO.

Always have Aircon on regardless.

[geoffdunk]

Does the outside temperature reading look ok? Mine sometimes goes mad and this affects how the heating/cooling works. This on a b7 by the way

Yep. Outside temp looks OK. I did a video for Audi so they could see it and the car gets colder on the inside but they are still saying its normal because the computer diagnostics didn't return any errors.

Here's the video: https://www.youtube.com/watch?v=BoFomg6sRlA

Sorry, a couple of things, you need it on AUTO, not just 21. With the system in Auto, all you need to do is press front demist and it will take care of things.

Also, how did you tuen on the wing mirror heaters?????? They come on with read demister, no button on the mirror adjuster knob. I though I saw you press the mirror adjuster or am I seeing it wrong? The know needs to be in the right turned location, i.e. the little mirror demist log, but there is no press function.

[moonigan]

Does the outside temperature reading look ok? Mine sometimes goes mad and this affects how the heating/cooling works. This on a b7 by the way

Yep. Outside temp looks OK. I did a video for Audi so they could see it and the car gets colder on the inside but they are still saying its normal because the computer diagnostics didn't return any errors.

Here's the video: https://www.youtube.com/watch?v=BoFomg6sRlA

Sorry, a couple of things, you need it on AUTO, not just 21. With the system in Auto, all you need to do is press front demist and it will take care of things.

Also, how did you tuen on the wing mirror heaters?????? They come on with read demister, no button on the mirror adjuster knob. I though I saw you press the mirror adjuster or am I seeing it wrong? The know needs to be in the right turned location, i.e. the little mirror demist log, but there is no press function.

Setting it to 21 is what Audi asked me to do so that's why I did it. I'll certainly try it on auto but previous attempts when setting the temp to hi and front demister on gave the same results. The wing mirror heaters, I thought that if the button was in the adjust position (either left or right) then they didn't come on so I was simply checking this. The push was for dramatic effect to emphasise that I had done something

The key thing I need to find out is if other B8 owners cars will blow out hot air first thing after the car is warm but still stationary. If this is the case then I can go to Audi and say here are some owners whose car doesn't do what mine does so please fix it.

[geoffdunk]

21 or 22 or even 19, thats not critical. Yes, mirror button needs to be in demist position, you are correct. It just so happens you caught me on a lazy day and my car hasn't moved this morning and is still sitting in the shade, frozen and misted up, I started the car and the screen was demisted and de-iced in under 8 mins.

AUTO will go off when you hit front demister and the fans will ramp up by themselves, there is no need for you to touch fan or temperature speed. You will not get hot air, you will get dry air, this is what you are after, the is what demists the screen on cold start. Now, if you are not getting rapid demist, then the question maybe are you getting dry air? At normal operating temperatures how cold does your system blow when asking for LO as there could be an issue with the condensing unit?

I just did 2 videos of mine going through the process, one on cold start and the settings and the other with it cleared and ready to drive. No hot air was blown, just dry.

Hot air is not supplied becasue the system is trying to heat the engine and all its parts before you get hot air into the cabin, this is what modern vehicles do to be more efficient. You will not get any hot air until the diversion valve switches it to the heater matrix. You do however get instant dry air which clears the screen before temperatures are up.

[HPsauce]

I don't know the specifics of your car but in general Audis (and other makes) will have a temperature sensor in the HVAC input plumbing that means they won't try to blow cold air into the car if that is what is otherwise needed. Hence (as described above) the fans often don't ramp up immediately on a cold start with normal settings.
The demist setting will generally override that and, as noted above, at least dry the air and increase the fan speed.

Does your model also have an auxiliary coolant pump, rather than just depending on the main water pump to circulate into the HVAC unit? If so maybe there's a minor issue there?
(Though on my S8 I've disabled that as it gets horribly noisy as the pump motor gets old; no noticeable difference)

[moonigan]

21 or 22 or even 19, thats not critical. Yes, mirror button needs to be in demist position, you are correct. It just so happens you caught me on a lazy day and my car hasn't moved this morning and is still sitting in the shade, frozen and misted up, I started the car and the screen was demisted and de-iced in under 8 mins.

AUTO will go off when you hit front demister and the fans will ramp up by themselves, there is no need for you to touch fan or temperature speed. You will not get hot air, you will get dry air, this is what you are after, the is what demists the screen on cold start. Now, if you are not getting rapid demist, then the question maybe are you getting dry air? At normal operating temperatures how cold does your system blow when asking for LO as there could be an issue with the condensing unit?

I just did 2 videos of mine going through the process, one on cold start and the settings and the other with it cleared and ready to drive. No hot air was blown, just dry.

Hot air is not supplied becasue the system is trying to heat the engine and all its parts before you get hot air into the cabin, this is what modern vehicles do to safe fuel and be more efficient. You will not get any hot air until the diversion valve switches it to the heater matrix. You do however get instant dry air which clears the screen before temperatures are up.

Superb thanks!! 8 mins is the ball park from what I remember previously. That answers the question about hot air and I've had no complaints over blowing cold air through the air con so I suspect I'm not getting dry air but rather air sucked in directly from outside which would possibly explain the drop in inside temp to match outside temp.

I will try the Auto process in the morning and report back. Thanks again.