My '92 500SL has problems with the heating/demisting sytem. It sometimes seems to work and sometimes doesn't. This is particularly annoying when trying to demist the windscreen and there is little or no hot air flow. Sometimes the air will start to flow after a few minutes, sometimes it won't.

Occasionally the system will work perfectly! I'm pretty sure it's not just the rotary switch that's at fault. Presumably this switch controls some sort of valve or something.

I recently had the aircon recharged and coincidentally the heating/demisting seemed to be fine for a while afterwards, but I can't see why this may have had an effect.

I've spoken to my tech' who said he won't know what the problem is 'til he strips it down! Perhaps someone here has had this problem and can offer some advice.

Hoping for response!

Kenny