Phaeton HVAC trivia

I was looking for a picture of a diesel car with smoke coming out the back end but found this instead.  Isn't it much cooler?

Outside the horse track yesterday, I was following an old W123 sedan.  It was accelerating and spewing out tons of black soot.  I held my breath, but then realized-- outside air wasn't coming inside the cabin.  The Phaeton had automatically switched to recirculating air.

1. The Phaeton is equipped with an air quality sensor (G238).  It's right next to the fresh air intake.  When it detects pollutants outside, it closes the air flow flap and opens the air recirculation flap.

The sensor contains an oxide mixed with tungsten.  The compound changes its electrical properties when it comes in contact with oxidisable or reducible gases.

Oxidisable gases include carbon monoxide, benzene vapors, petrol vapors, hydrocarbons, and unburned/incompletely burned fuel components.  Oxidisable gases absorb oxygen and bind it.  When the sensor comes into contact with an oxidisable gas, the gas absorbs oxygen from the mixed oxide.  This changes the electrical properties of the mixed oxide in the sensor, and resistance falls.

Reducible gases include nitrogen oxides.  Reducible gases pass oxygen to other elements or compounds.  When the sensor comes into contact with a reducible gas, resistance rises.

If the measured resistance deviates from the default value, then the air conditioner control unit concludes that the ambient air is contaminated and starts up the automatic air recirculation function.

2. Every time the Phaeton is shifted into reverse, the recirculation function is turned on automatically so that exhaust gases do not enter the cabin.

3. And here are all 25 of the motors used to circulate air inside the cabin:

Air conditioner 

- air flow flap control motor 

- defroster flap control motor 

- air recirculation flap control motor 

- control motor for front cold air flap 

- control motor for front warm air flap 

- control motor for left footwell flap 

- control motor for right footwell flap 

- control motor for front right shut-off flap of defroster and chest vent 

- control motor for front left shut-off flap for defroster and chest vent 

- control motor for rear right centre console warm air flap 

- control motor for rear left centre console warm air flap 

- control motor for rear right centre console cold air flap 

- control motor for rear left centre console cold air flap 

- control motor for right B pillar and footwell shut-off flap 

- control motor for left B pillar and footwell shut-off flap 

Dash panel 

- control motor for right defroster/chest vent flap 

- control motor for left defroster/chest vent flap 

- control motor for indirect ventilation air flap 

- front left centre vent 

- front right centre vent 

- control motor for left design panel 

- control motor for right design panel 

- control motor for centre design panel 

Rear distributor housings 

- rear right footwell/defroster flap control motor 

- rear left footwell/defroster flap control motor