I had similar problem... but I forget the exact symtoms. My problem was with the control knob that sets the desired interior temperature. I took my controll panel apart ... examined it carefully till I figured out how it worked... I found the problem and fixed it. If I recall.. it had sometning to do with a crack in relation to the temperature knob (wheel).
1993 190E 2.3
2000 Toyota 4x4 Tundra