Some from http://www.mercedesmedic.com/ac-air-conditioner-diagnostics-with-trouble-codes-list/
Some from http://www.benzworld.org/forums/w210-e-class/1384396-automatic-climate-control-diagnostic-trouble-code.html
Additions from some other places.
Some updates by me to reflect what works in my 1999 E300, US version with Automatic Climate Control.

How to troubleshoot Mercedes Benz Air Conditioner System, Read Sensor Data, Reset Unit 
Troubleshooting Instructions 
Entering Diagnostic Trouble Code (DTC) Display Mode 

Preparations for DTC readout:

Ignition ON (position 2)
Auto mode OFF (use mode buttons to change from Auto to manual selection)
Set temperature selectors: left to "HI", right to "LO".
Within 20 seconds, press REST and EC simultaneously for more than 5 seconds.
The REC button LED flashes (the display goes blank).
Press AUTO to display first DTC. Press AUTO repeatedly until all DTC's (refer to DTC table) are displayed. Record each DTC as it is displayed.
Each malfunction (short circuit, open circuit, etc.) has a specific DTC assigned to it.
The letter "E" (Error) is displayed in the left side of the display and the DTC is displayed in the right side of the display. By pressing the right AUTO button, the next DTC stored in memory will be displayed.

To erase: Only possible after all DTC's are read out. Simultaneously press both AUTO > 2 secs. "d" will be displayed in the left side of the display window and "FF" on the right side.
To cancel erase: By pressing AUTO the current faults will appear again.

Reset temperature selector to normal setting.
Turn ignition OFF to end test.

DTC table:

B1226 - In-car temperature sensor (B10/4)
B1227 - Outside temperature indicator temperature sensor (B14)
B1228 - Heater core temperature (B10/1)
B1229 - Heater core temperature (B10/1)
B1230 - Evaporator temperature sensor (B10/6)
B1231 - ECT sensor (B11/4)
B1232 - Refrigerant pressure sensor (B12)
B1233 - Refrigerant temperature sensor (B12/1)
B1234 - Sun sensor (B32)
B1235 - Emissions sensor (B31)
B1241 - Refrigerant fill
B1416 - Coolant circulation pump (M13)
B1417 - Duovalve (Y21y1), left
B1418 - Duovalve (Y21y2), right
B1419 - Electromagnetic clutch (A9k1)
B1420 - Idle speed increase
B1421 - Pulse module (N65)
B1422 - Series interface (K1) connection to instrument cluster (A1)
B1423 - Switchover valve block (Y11)
B1424 - Activated charcoal filter actuator (A32m2) open
B1425 - Activated charcoal filter actuator (A32m2) closed
B1432 - Non-USA DTC B1459 - Series interface (K2) connection to instrument cluster (A1) 
B1459 - Series interface (K2) connection to instrument cluster (A1)
B1462 - Wide open throttle (WOT) position signal: diesel engines

Climate control as a diagnostic tool
READING SENSOR VALUES

1) Turn ignition on. Simultaneously press down and up arrow push buttons until the pre-selected temperature setting of "72 °F" is displayed. Press the AUTO push button. 

2) Press REST push button for more than 6 seconds. The display window will show "1" on the left, and on the right an in-car temperature of "72 °F", or "LO" if there is an open circuit, or "HI" if there is a short circuit. 

3) By pressing the windshield air distribution push button, the next ascending test step is displayed. By pressing the footwell air distribution push button, the next descending test step is displayed. See SENSOR VALUE DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION table. Press REST push button to exit reading sensor values mode.

01 = In-car temp sensor
02 = outside temp sensor
03 = left heat exchanger (heater core) temp sensor
04 = right heat exchanger sensor
05 = evaporator sensor
06 = coolant temp
07 = refrig. pressure in bar
08 = refrig temp sensor (23*9 = 23.9deg C)
09 = nothing
10 = Blower control voltage (great for evaluating blower controller problems)
11 = emissions sensor (B31) e.g. 3.1 = 31.v
12 = sun sensor 4.2 = 4.2v
20 = aux fan control 6.1 = 6.1ma (max 10ma)
21 = engine speed22 = vehicle speed
23 = Circuit 58d e.g. 99 = 99% of battery voltage
24 = BATTERY VOLTAGE e.g. 12.5 = 12.5v
30 = left rear air conditioning heat exchanger temp sensor (not all vehicles; obviously)
31 = right side
32 = rear evap temp sensor
33 = blower control voltage rear 0.8(MIN) – 6.0(MAX)
34 = left rear temp selector
35 = right side
38 = software status e.g. 37 rear air conditioning
38 = hardware status e.g. 37 , rear air conditioning
40 = control module version software status (?)
41 = control module version menu hardware status
42 = control module variant code 1st number
43 = variant code second number.

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