I will assume that you are speaking of the climate control and will answer accordingly...The temp sensor is two part. It is located in the dome lamp assembly. There is a temperature sensor and an aspirator motor. The aspirator motor pulls the air over the sensor so it does not heat sink. Make sure it is pulling.

Do this by ripping a small piece of paper and see if it will hold to the little vent that pulls in the air.

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Benzmac:
Donnie Drummonds
1992 500E (very soon I hope
1981 280GE SWB
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM