Found it. Its under some electronics and a hood switch. I will dig it out in the morning and see whats up with it.

There is one brant, MTC, any good? They do not get a good review from Pelican. But for this part, are they an option? OEM is over $100 for a rebuild kit!

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

All I could find was the MTC. If you buy it from Pelican Parts above its only +$15. It is worth a try...I did

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'89 300SE
'02 E320 Wagon

I am curious. What does that switch do? I have been searching to find out but to no avail.

I know you replaced the monovalve but it still has the symptoms of a bad monovalve. My car did the same thing; some heat at low speeds and no heat at highway speed. The diaphram was damaged. I installed a MTC monovalve and it worked correctlly. It has been about 6 months now and it is still working fine. Maybe try another cheapie MTC monovoale, seems they might be a little hit&miss as far as working right.

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1986 560 SEL
1960 Ranchero
1970 Cougar XR7
2002 Crown Vic Sport
1992 F150