Take the sensor out and test it. It should give a certain Ohm resistance based on the ambient air temperature. You can move the sensor from outside to inside to see if the unit is working correctly based on varying temperatures.
If you do chose to move it you could place it under the passenger knee bolster. That is the location of the tube connection to the blower motor. a flexible hose could be used and mount the unit in a hole you will make in the under dash panel. The air would still be drawn over the sensor via the tubes you would connect to the current blower motor setup. Drop the passengers under dash panel and figure out where you would like to mount it. To access the sensor unit remove the glove box interior and pull the blower motor tube as well as the 2 connecting wires. then the unit is pulled out of the dash towards the rear view mirror

Yes the picture shows the windshield side at the top and the black tube moves from the center of the dash to the passenger A pilar area.

Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car