86 325e heater problem

This is my first post... ok i have a 1986 325e and my heater doesnt work. It used to be nice and warm but after christmas break, it stopped working. The car warms up, but no heat, only regular air comes out(in the mornings, its COLD). Anyone know what could be wrong? Tell me if you need any other info, Thanks.

-Max

my dad's 635 had a very similar problem, and apparently, it was soming thing having to do with the sensor in the dial. i would just take it to a shop, and they'll probably fix it for pretty cheap