I am having a weird problem with my 1996 C220 where my 'heat' is blowing cold air unless I set my temperature control to 'HI' whereas I get heat. I had initially thought it was my heater core, but since I do get heat on the 'HI' setting, I guess that would rule that out. I am thinking it could by my 'ACC Dual Valve'
Auto Parts Warehouse Product Catalog - 1996 Mercedes Benz C220 ACC Dual Valve
located under the hood, under the plastic compartment in front of the passenger side, but I want to be sure before shelling out the money for a new one.
I also have another problem which I think is related...or causing this one...but can't be sure. I often hear the vacuum pump 'whirring' in the trunk of the car and I believe that it controls the servos of the climate control. If this is the case, then I am thinking I might need a new climate control unit being that it's not properly controlling the servos and thus, not getting heat until (for some reason) it's put on HI.
Any help is greatly appreciated!
This past weekend I replaced my duovalve and auxillary pump, my douvalve was making the ominous thumpety thump under the dash for quite some time and finally had a window of time to address both my coolant change and quirky noise problem when the heat was on.
(yes I did change out the thermostat to and did a flush since it was undergoing a bypass operation) . There have been a few posts on how to rebuild the duovalve, personally my time is worth more, I'll leave that choice up to you. What happens to the pistons inside of the valve is that they can stick after years of use as well as the internal rubber parts wear not making a good seal, also the solenoids can go bad.
The auxillary pump was changed as a preventative measure since I really have no idea how old it was. Vehicle had about 58000 miles on it when purchased used, now has 92000.
I doubt your climate control is bust unless you are having both heating and a/c issues. It would be good measure to look under the dash and listen for any hissing from broken, loose, or disconnected vac lines.
The duovalve is a real tricky one to do on the c230 unless you want to yank a bunch of stuff out of the way, big hands are not helpfull for this particular job. If you can hire someone with small hands I am sure they would not get as sore as I did.
One of the signs you can look for to confirm the problem would be to open the hood while the heater is on (in your case full blast) and feel the two cylinders of the valve for a tapping on both sides, mine only did it on one side and actually made the lower radiator hose do a bouncing movement like a dangling sausage.