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Todays Factoid - Overengineered HVAC


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From time to time we find out questionably interesting things during our core business which we feel a pressing need to share with someone. The wifes not interested, and the kids dont understand so its your turn +++

For those that own Vagcom, or the shareware equivalents, you have a feature called measuring blocks. This lets you connect to a particular controller and view what information it knows. For example, the Engine ECU knows engine speed, timing, temperatures, the navigation can tell you what wires / aerials are connected and the instrument cluster can tell you everything from fuel level in litres to current battery voltage

- but -

the HVAC (Heating Ventilation and Air Conditioning) takes the prize for the largest number of misc bits of info. Lots of different flaps, with degress of rotation, temperatures of coolant, airways, vents and other a/c related items.

So, it was a curiosity when we discovered that the HVAC unit has an input to know when you are washing your windows. Not wiping, but actually when you have the squirter spraying water.

What can i say, it was a long trip to Billing yesterday and with time to kill a session with Vagcom commenced.

After a number of theorys had exhausted, we proved without a doubt that the HVAC unit uses this information to automatically switch your ventiliation onto recirc mode whilst the jets are being operated. How long, depends on your settings. If you have the Climate module on Auto-Recirc anyway, then it will spend 2 minutes on recirc after squirting. If you have it on fresh air only, the it will recirc for 20 seconds.

This was done on a Post facelift car, but it wouldn't suprise me if its the same for preface. We're not 100% why they did this. We doubt its for water ingress, so our only theory is that it was done to stop the smell of the sreenwash from entering the cabin ?

Its very effective - once we discovered this we realised we've never smelled the screenwash whilst in an A8 - and you never will.

So, bin the expensive posh fruity fragrance as it can only be enjoyed by the folks behind you... +++

Another money saving tip from A8 Parts.... :)

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When the notoriously fiddly connector pipe is secure, the jets are pretty powerful so the water ends up on the roof and the side panels. I don't know if there is a paint friendly screen wash but I just keep the glass squeeky clean by claying it regularly to remove contaminants and clean the wiper blades so all I need is water when the birds do thier thing.

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