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David Kingsbury 01-02-2001 07:58 PM

After reading through past heating problems I have determined that the MONOVALVE must be my lack of heat problem. What I donít know is its location. Can some one tell me where it is? Also where is the air-intake for the heating and cooling system on this car?

The problem is I have no heat at all. I have plenty of coolant. I do get some heat if I squeeze the water line between the intake manifold and the firewall. I have also looked at the water pump to see if there was a typical thermostat. I didnít see one. However, I also did not see where one would have been installed. My assumption is the car does not have one. Is this correct?

Thank you,

David Kingsbury
88 560SEL
67 European Beetle
69 Conv. Beetle
00 Dodge Durango

mbdoc 01-02-2001 09:57 PM

Under the hood, about 1 foot to the drivers side of the battery. Has 4 screws holding the solenoid to the body of the valve.

David Kingsbury 01-04-2001 06:09 PM

monovalve and mystery part
Thank you for the information. I found the monovalve and it has a tear in the large diaphragm.

Second thing I did notice is a broken part. Just above the monovalve is a bracket that holds a black device with a small button and a red light. On that same bracket I have a part that is broken. It has two wire attached with separate connectors. All that is left of the part is the two wires a spring up the center of four prongs. The housing and the rest of it are gone. It looks like it has been that way for a while. Any idea what this is so that I can get it replaced?


BlackE55 01-04-2001 06:49 PM


I believe it's center/pass side right up towards the firewall. I had this same problem last weekend. Blew air, but not hot. It would blow hot air *only* after it sat for a few minutes, then would blow outside temp air again.

Ted Edin

1991 560SEL
1970 Toronado GT
1966 Toronado Deluxe

David Kingsbury 01-04-2001 07:44 PM


How did you solve your problem? I have a similar circumstance. My car will blow warm air after I turn the engine off and then back to cold when it is running.


BlackE55 01-05-2001 01:23 PM


The part is called a "mono water valve".

A plunger that closes off the A/C from the heat (I think). The whole piece is set with 4 screws. If the plunger (aka valve) clicks as it did in my case, it's bad. A fairly common problem.

Hope this helps,


robaincltnc 01-05-2001 10:59 PM

Don't they make a repair kit for the monovalve? I need to do this repair to my 560sl.

BlackE55 01-06-2001 11:02 AM


I wouldn't doubt it, but...

The part in question (valve) was simply swapped with a good part. Took all of 10 minutes to do and the heat was back to normal.

-Ted Edin

'91 560SEL 101K miles
'70 Toronado GT (400 HP, 1 of 5,000 produced)
'66 Toronado Deluxe

[Edited by w126 on 01-06-2001 at 05:49 PM]

David Kingsbury 01-22-2001 07:16 PM

I replaced the MONO valve for $40.00 and the heat works perfect. If any one would like details of how I did it. Please feel free to email me.



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