ACC problem in 1993 300E
 

Apologies for making my first post a problem, but I have a problem with the ACC system in my 1993 300E2.8 that I can't quite diagnose.

First of all, there's no warm/hot/cold air coming out of any of the vents at all unless I push the 'EC' button, then I get some warm air when travelling at speed. Secondly, when I push 'defrost', 'bi-level', or 'normal' there's a squeal which I originally attributed to a siezed blower motor, but when I pulled the blower motor fuse and tried the ACC again I got the same squeal.

After some investigation, the squealing seemed to come from the heater control solenoids (close to the battery), and I know they're a common problem with the 124's, but I thought that these controlled hot water flow to the heater core and I'm puzzled as to why I don't get cold air from the air conditioner. Plus, why do I get warm air out of the vents when in 'EC' mode and at speed?

Perhaps I'm completley off - could it be the AC compressor, or the auxiliary water pump, but if so, why does the squealing come from the solenoids? And why does my blower motor not seem to be pulling air in regardless?

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

I'm afraid I can offer no assistance but maybe sooner or later someone can. We have some extremely smart people here. My only thought about something "squealing" makes me think a belt is slipping...

and of course the movie Deliverance

That was my first thought too - but if it was a belt on the air conditioner, why do I get no heat, and if it was coming from the aux. water pump, why do I get no cold air? And what's in the heater control solenoids that would cause the squealing?

93 400 e with similar problem
 

I have similar characteristics but my 15 amp fuse was blown. I have taken out the blower fan which is located about an hour underneath your wndsheild wiper assembley. My fan worked outside the car so I took out the controller located under the fan. I test the connectors on the fire wall and found ground and 12 volts on the red and yellow plugs. I am assumming I need a new controller. Your situation sounds a lot like mine. Test the fan out of the car and check the other voltages. My system slowly stoped blowing air but seams to function otherwise. Cold gets cold hot gets hot.

Chris

I did start to remove the blower motor over the weekend, but when I realised that the squealing wasn't coming from the blower motor (the squealing was present with or without the blower motor fuse), I stopped and reassembled the car. Plus, it wasn't a slow reduction in the amount of air movement - one day the ACC worked, the next day nothing (except the squealing), and a very unhappy SO (she drives the car daily, not me).

I'm happy to replace the blower motor or the solenoids myself, I just don't want to start replacing random parts in the hopes that I get the right one - especially when I'm not convinced it's the blower motor (unless someone can persuade me that the motor will still squeal even with it's fuse removed).