Looks like everyone passed over my request for help (and yes, I did search the forums, but there was nothing similar to my car's symptoms), so here it is again.

My 1993 300E2.8 with 155k has no working ACC - no heat, no cold, nothing, unless in 'EC' mode and travelling at speed.

When I do try and use the ACC, I get a squealing from the heater control solenoids (sometimes known as 'monovalves') that's loud enough to be heard inside the car. I thought it was the blower motor making the noise, until I heard the same noise with the blower motor fuse removed.

What's puzzling me is the complete lack of airflow, either hot or cold - if the monovalves were the problem why do I not get cold air from the A/C?

Maybe I'm on the wrong track completley and it's the auxiliary water pump, but surely I'd still get some warm air and cool air? Could it be the ACC PBU? It does have a burnt out bulb inside it that needs to be fixed.

Does anyone have any suggestions for a DIY repair before I turn the car over to the dealer for them to look at? This problem has me puzzled