Odd thing....

[milleplod]

I noticed something odd about my '09 C5 2.0hdi Tourer t'other day. When I put it into reverse.....the interior blower/fan speed increases! I've tried, really tried, to think of some (French!) logic that might have been applied when the car was designed, but have come up with nothing!

Any ideas anyone?!

Pete

[Stickyfinger]

Screen clearing, it switches on AirCon as well I think.....my one does the same

[milleplod]

Ahhhh......definitely French logic then!.....I need to see more when going backwards! 'Surrendering' rings a bell....

Thanks for the reply!

Pete

[white exec]

Gosh. Wow.

[GiveMeABreak]

This is part of the function of the Dual Zone Automatic Air Conditioning system. It uses an air quality sensor to automatically switch to recycled air when it detects pollutants, thereby preventing them from entering the cabin. Great for traffic lights or queues. It is not available on the Monozone systems. It doesn't operate below 5 degrees though - to prevent misting. It's on page 101 of the 2008 C5 Owners Handbook - but generally under that section for later manuals. That noise you can here is the switching of the flaps to cut off the outside air and the slight increase in fan speed to ensure adequate circulation of air in the cabin.

It's just a shame the sensors aren't clever enough to detect nasty niffs!

[Stickyfinger]

I do have to say, it does seem like a good thing to me and not at all strange.................

[Paul-R]

It's just a shame the sensors aren't clever enough to detect nasty niffs!

Those usually emanate from inside the car and need as much outside air as soon as possible!

[GiveMeABreak]

It's just a shame the sensors aren't clever enough to detect nasty niffs!

Those usually emanate from inside the car and need as much outside air as soon as possible!

Not unless you've got the latest tech Paul!

[Paul-R]

I noticed something odd about my '09 C5 2.0hdi Tourer t'other day. When I put it into reverse.....the interior blower/fan speed increases!

Blurryell - so does mine! Never noticed that before.

[milleplod]

I do have to say, it does seem like a good thing to me and not at all strange.................

I think I follow the logic of it happening, its a clever idea I suppose....but, let's face it, most people don't spend long enough in reverse for the increased fan speed to have any effect whatsoever! By the time I've reversed off my drive, for example, or slotted into a parking bay, the fan's been blowing a bit harder for all of 10 seconds.....And, why did whoever came up with the idea think that the fan speed should increase just because I'm going backwards?!

Seems more like something 'for the sake of it', rather than there being an identifiable problem existing that needed fixing.

Pete

[GiveMeABreak]

It doesn't just happen in reverse Pete - as I said in my last post it happens whenever the air sensor detects pollutants in the air. When the switch over to recycled air is in effect, the fans speed up to increase the circulation of the air in the cabin as it is 'stale' air.

[milleplod]

It doesn't just happen in reverse Pete - as I said in my last post it happens whenever the air sensor detects pollutants in the air. When the switch over to recycled air is in effect, the fans speed up to increase the circulation of the air in the cabin as it is 'stale' air.

Got that! I've done only 1k miles in mine since buying it....the fan speed increases every single time I put it in reverse. Is there some 'logic' being applied to make that happen? Is the car perhaps detecting pollutants when I select reverse?

Pete

[GiveMeABreak]

In addition to switching on when it detects pollutants under other conditions, it may well be kicking into that mode on reverse automatically as typically when reversing you will inevitably be sucking up spent exhaust gases as you move backwards. I've often been driving, stuck in a traffic queue and it has changed modes - usually behind an old bus! Shame it doesn't pick up chip fat - there's been a few times I've been stuck behind one of those for a while!

[Richard_C]

It has a curious logic all of its own. Its not just fan speed, it goes into 'recycle' mode in some circumstances. If you peer at the AC display and press the recycle button you will see it has 3 states, off, on and auto (if you press auto on the main temp dial it goes to auto anyway). When it is on auto it switches to recycle if it thinks you are in a traffic jam but changes back if it goes on for too long so you don't go drowsy through lack of oxygen perhaps, if you reverse presumably so you don't suck exhaust fumes in, and most oddly if you squirt the screenwashers. I guess that's useful in colder climates when you have 50% alcohol in the wash bottle so you don't inhale the fumes.

(at least mine does, but I have a theory that the factory is allowed to have a bit of fun and do what they want on some days so they all come out a bit different)

[vborovic]

It will also recirculate air after using the windscreen washing fluid ... no fancy logic there, just pure mechanics coupled with the BSI and a few code programmer's IF-THEN loops ...