It may be that your evaporator temperature sensor has failed. Have a look at these threads to check your symptoms:

http://www.peachparts.com/shopforum/showthread.php?t=120267&highlight=evaporator+temperature+sensor

http://www.peachparts.com/shopforum/showthread.php?t=84047&highlight=evaporator+temperature+sensor

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JJ Rodger
2013 G350 Bluetec
1999 SL 500
1993 E300 diesel T
1990 190