I'm having the same problems with my 2000 CLK430 Cab....The outside temp reads -37...It's really getting to me....
Anyway , I went to mouser and looked for the thermistor and allot came up, I just don't want to get the wrong one...

Here is the link to Mouser:
http://www.mouser.com/search/Refine.aspx?Ne=1447464+254016+1118567&N=1323038+4294829681+0&Ntt=*3K*+*thermistor*&Msb=0&Mkw=3K+thermistor

Thanks for the help this Forum is awesome!
///Michael