I never knew this feature existed until a few days ago...and there seems to be no Audi resource for a complete list of code functions (that I could find?).
Anyway, with ignition on (engine running or not) and climate control on, press upper vent button on driver's side and recirculate button simultaneously. The code # will appear on driver's side temp window and associated value appears in passenger's side temp window. You can scroll through codes 1-149 with "+" or "-" buttons on drivers side. Below you'll find the best reverse engineered list of code designations and associated value numbers.

This is all for Facelift D2 A8/S8.

From what I've found, many (if not all?) climate control systems on VW/Audi from mid-90's on "should" have a similar feature, but possibly with different button combinations to activate it AND completely different codes for diagnostic functions. When I Googled "Climate control secret codes VW/Audi" , I found lots of info on other models, so if you don't have a FL D2, have a look there.

Have fun.

Also, here's a link to the original thread from 2005:

http://forums.audiworld.com/showthre...+control+codes

10 Center vent temperature thumbwheel -G142-

For each line in the group below,
first address: actual flap position, corresponding to field 1 in the display group
second: specified position as a percentage of open, can be changed with the fan -/+ buttons. These values persist after returning from Defog. Pushing Auto returns them to defaults.
third: basic settings closed flap value
fourth: basic settings open flap value
11, 12, 74, 75 Temperature regulator flap motor -V68- [heated air to center vent], display group 6
13, 14, 76, 77 Left center vent motor -V110-, display group 3
15, 16, 78, 79 Center vent adjusting motor -V102- [unheated air to center vent], display group 5
17, 18, 80, 81 Right center vent motor -V111-, display group 4
19, 20, 82, 83 Rear footwell [console] vent motor -V119, display group 9
21, 22, 84, 85 Left footwell flap motor -V108-, display group 7
23, 24, 86, 87 Right footwell flap motor -V109-, display group 8
25, 26, 88, 89 Defroster flap motor -V107-, display group 2
27, 28, 90, 91 Airflow flap motor -V71- [fresh air intake], display group 10
29, 30, 92, 93 Recirculation flap motor -V113-, 0% = open, display group 11

33 Speed km/h
34 Fresh air blower -V2- actual voltage, display group 16 field 2
35 Fresh air blower -V2- specified voltage, display group 16 field 1, adjust with fan -/+ buttons
36 Voltage in
37 Voltage in

41 What the fresh air blower voltage would be in AUTO
42 Fresh air blower -V2- specified voltage as in 35, not adjustable

49 Unscaled battery voltage, about 175 engine on, 155 engine off, lower during cranking
50 as for 49

54 Display illumination percentage, depends on instrument cluster brightness sensor and buttons, display group 16 field 3
55 Button illumination, depends on instrument cluster brightness sensor and buttons. 0 with parking lights off. Twice the percentage in display group 16 field 4.

59 rpm/10

64 0-255, larger = more cooling or less heat demand

68 Heating demand satisfaction, 0-255. Heat regulating valves -N175- and -N176- stay closed when this reaches 255.

72 Recirculation flap motor -V113-, specified position % closed, follows 30 but not adjustable
73 Airflow flap motor -V71- [fresh air intake], specified position % open, follows 28 but not adjustable

74-93 see 11-30

102 Coolant temperature from instrument cluster
103 Appears to follow 107
104 Instrument panel interior sensor -G56-
105 Fresh air intake duct temperature sensor -G89-
106 Outside air temperature sensor -G17-
107 The lower of -G89- or -G17- values
108 Left vent temperature sensor -G150-
109 Right vent temperature sensor -G151-
110 Sunlight photosensor -G107-, left, % as reported in display group 15 field 3, but can go over 100
111 Damped left sunlight value, follows 110 slowly
112 Left sunlight value as a percentage of right sunlight value, 255 if no right sunlight
113 Sunlight photosensor -G107-, right, % as reported in display group 15 field 3, but can go over 100
114 Damped right sunlight value, follows 113 slowly

120 0-255, larger = more cooling or less heat demand, slowly adjusts to sunlight without regard to its direction
121 appears to follow 120

123 appears to follow 120, taking into account damped left sunlight value

125 appears to follow 120

127 appears to follow 120, taking into account damped right sunlight value
128 appears to follow 127

 

Silver,
Stupid thing started working last night on my last 5 min of the drive. A cupple min at around 90 did the trick. I heard a bunch of whining when it kicked on high but went away, I am expecting to have to pull it out and put a coat of shine and lube on it.

Just in case anyone is wanting to know, my blower motor quit working last night at the worst possible time, 20 outside and a bunch of fogged up windows.