its a cable thing,or more correctly a maladjusted cable due too wear........
i have never fixed mine i just push it forward with my finger.......
i dont have the radio box installed so it doesnt get in my way................
thr lever is located on the lower right side of the cable control box......
go to the lower right hand corner of the controll move your hand down about an inch and a half then go in about 3 inches {to fire wall} and you will find the levers the lever for the defrost isnt going all the way forward it just needs to go about a 1/4 inch more and the defroster will work.........
at least that is what i have to do ......i would think thats whats going on with yours .....
similars design failures are fun arent they........
i found out many moons ago that messing with the cables on this sort heater is not easy or fun .....

so just find a way to manualy push it forward and you will be farther ahead
