I don't have an answer for you but you can check this thread, post #9.

http://www.peachparts.com/shopforum/diesel-discussion/366117-w124-stumped-climate-control-unit.html

It could be the evap temp sensor behind the driver's kick panel. Try to time the cut-off time to see whether it is the same or very consistent. Good luck.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.