On my 300sdl I have great ac but no heat. Fan comes on and blows cold air. Engine comes up to temp at 80C.
I removed connector from monovalve and still no heat.
What next? thanks.

You have an obstruction somewhere. Investigate to find out where.

Check the mono valve.

Like above - take the monovalve out, inspect then clean or replace. After a summer of driving its very common for them to stick in the closed position. Its up on the center to passenger side firewall. Click parts and search for monovalve so you know what you are looking for. Be careful taking small screws out - very easy to fall into the crevice of never find (sound dampener).

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00 E420
98 E300 DT
97 E420 Donor Car - NEED PARTS? PM ME!
97 S500
97 E300D
86 Holden Jackaroo Turbo D
86 300SDL
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Thanks for the input. I was dreading digging into the monovalve, but it seems the most likely. Looks tight down there.

http://mbdieseldiy.tripod.com/monovalve.htm

I was hoping that I could repair in situ, thanks for the great link!

It is much easier to swap the monovalve than if this was some sort of airflow problem caused by the Push Button Unit or a pod underneath the dash. Monovalve takes a few minutes to change out, taking the dash takes a few days of nonstop working to get to all the pods.

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2009 ML320 Bluetec
1985 300CD
1981 300TD

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD

I will probably get flamed for this but generally when one sticks on my W126 a slight adjustment with a Whomp with a rubber hammer has worked. All said it's not anywhere near a complicated disassembly to clean or inspect.

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15 VW Passat TDI
00 E420
98 E300 DT
97 E420 Donor Car - NEED PARTS? PM ME!
97 S500
97 E300D
86 Holden Jackaroo Turbo D
86 300SDL
(o\|/o)

Consider yourself flamed.
I'll give it a whomp with my rubber persuader first.

I removed the top of the monovalve and the diaphram is torn. Doesn't a torn diaphram usually cause heat all the time?

Yes - unless the cylinder is closed. How does it look? Should be very close tolerance and be extremely shiny (clean). You probably know you dont need the entire mono valve just the repair kit (Part #W0133-1618202
)

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BENZ THERE DONE THAThttp://www.peachparts.com/shopforum/...c/progress.gif
15 VW Passat TDI
00 E420
98 E300 DT
97 E420 Donor Car - NEED PARTS? PM ME!
97 S500
97 E300D
86 Holden Jackaroo Turbo D
86 300SDL
(o\|/o)

It woudl be nice to know what year sdl!

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1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

It's an 87, didn't know there was a difference.

Back to the heat thing, with a torn diaphram, I should be getting uncontrolled heat. I get NONE. What are the symptoms when the aux pump fail?

With the failed diaphragm there are numerous possible outcomes often times constant heat but others have experienced no or irregular heat the safest thing is to replace the monovalve with the repair parts and then see if your problem still exists. You'd need a new repair part no matter what!