help on a rare one!!!

I live in Argentina and have a 1989 190 D, gourgeos. But there this mistery no one I consulted has been able to solve.
the three knobs for the air heater on the panel (middle one distributes air flow and the other 2 control temperature for each side) heat up (real hot it burns your fingertips)
it does this 98% of the times the car runs. I found out that what does this is a couple of little red hoses that come in and out of the back of the knobs, but i canīt figure out what they are for and why it heats up so much. it happens in warm or cold wheather ans in hot or cold operating temp.

if anyone has a clue of this please give me a hint. thanks.

Hi 190 D,

Do the knobs heat up when you have the lights on? If so the illumination bulbs could have been replaced by ones with too high a wattage. I think they should be no more than 0.4 watts. On my 300E the bulbs are tiny push-in types with frosted glass. I had replaced a heater knob illumination bulb with an apprently identical one but it glowed brighter than all the others! I can't remember if it heated up the knob too much but I replaced it with a genuine MB one because it looked odd. I have only found these at MB dealers but they are cheap (Ģ1 each I think). the part number for 124s is 000 825 00 99, the same for 190s? Are the red "hoses" you mention the bulb illumination wires? These may also get excessively hot with incorrect bulbs. If it isn't the bulbs then I hope you find out what it is.

Best
Ian

Ian: Thanks for the answer. In fact, the light bulbs are OK and they donīt heat up. The red hoses I mention are (I suppose) air hoses, since they donīt seem to have water. If disconnected, the knobs donīt heat up, even with the lights. if connected they heat up. I presume it may have something to do with heating up for cold wheather, before the water heats up, but I could not figure it up yet, since in hot temps it also heat up very much

thanks again for answering

testing