a/c ductwork
 

89 560 sel, would anybody have a diagram of the ductwork on this vehicle? compressor is running, r-12 is flowing, blower motor blowing, but only warm to hot comes out of the vents. Is the heater core and the evaporator on the same duct? or does the air get blown through different ducts for heat than a/c???? switches and vacuum valves seem to be working to put air out vents in dash or defog or floor....any ideas?

I'm sure someone more knowledgeable than I about ACC function will weigh in on this, but if air is coming out of the appropriate place (e.g., out of AC vents if cabin temp is higher than the temperature on the dial) but is warm instead of cold, probably a stuck open monovalve. I've had no personal experience with them, but as I recall, when they go bad, they may stick open and send hot coolant to the heater core all the time.

Might do a search on "monovalve" and see what pops up.

thanks for the suggestion on the monovalve, but that (replacing the monovalve because of no heat, but a/c worked fine) is when the a/c quit blowing cold. i'm starting to think the new valve might not be closing properly?

So the AC was working OK until the monovalve was replaced? I agree, sounds like that's the culprit. Can you feel the heater hose coming off the monovalve into the heater core? If it's hot, but the system should be cooling, that would mean that the system is inappropriately sending hot coolant to the heater core when it's not supposed to. I suppose the problem could be upstream of the monovalve (e.g., a problem with the pushbutton control panel) but I'm out of my league here. Just a thought, though -- are you sure all the vacuum hoses got replaced when the monovalve was replaced? I understand that, for safety reasons, the default setting for the climate control is full heat, so I'd assume that if a vacuum hose (or wire, I don't know how it's controlled) is left off, it would default to full heat.

Hopefully someone with more knowledge than me will respond . . .

If no one else responds, you might want to re-post this with a different subject line, like "heat on full time" or some such, since some folks who could be helpful might see the "a/c ductwork" subject and pass over it.

1988 560SEL
 

While we are on this subject, My SEL has a vent between the seats for rear airconditioning. I nomally only use the car in summer but had a chance to use it when it was cold out. I get excellent heat in the car, but the air coming out of the center vent to the backseat blew ice cold air on the ladies in the back seat. Turning the vent off corrected the problem. Is this normal?. Is this vent not designed to blow hot air?
Thanks

Yes, on the w126 models, the rear seat a/c vent only blows cold year-round. Heat comes from ducts under the seats (as it does on other models, too.)

Time to get out your voltmeter and check for battery voltage across the two pins on the monovalve,this should be done with temp wheel on min. and center button pushed on pushbutton assy.
If you have 12 volts across these terminals valve should be closed.
I saw in your post that mono valve core was recently replaced,if the steel sleeve around the magnet coil is not properly aligned (there is a notch that should align with the point where the magnet wire comes through) it can cut the magnet wire.
if the wire is cut it's time for a new assy.
MF