I would think it's not likely to be the sensor, but it is easy to check. Measure the electrical resistance at room temp. Then heat it up to 90 degrees or so and measure it, then stick it in the refrigerator to take it down to 40 degrees or so and measure it again. If you can see the resistance change with temperature, the sensor is probably OK. Climate control manual probably has a table showing what the resistance should be at any given temperature (Centigrade, of course). If it's like a 123, sensor goes to the acc control unit. 123 acc manual shows how to test the controller with a special tool, but, by reading between the lines you can figure out how to test it manually.
P.S. Smoke from a cigarette makes a good quick check to see if the hose is drawing air. Might be easier than the paper method.
2004 C240 Wagon 203.261 Baby Benz
2008 ML320 CDI Highway Cruiser
2006 Toyota Prius, Saving the Planet @ 48 mpg
2000 F-150, Destroying the Planet @ 20 mpg
And remember folks, Only You Can Prevent Hilliary.