Interesting... I forgot your car has that silly mono valve.. Mine has an either open or closed heat valve that is vacuum operated. Whenever heat is needed it is open fully, only closes when the temp wheel is set low enough and the outside temp is above the selected temp. I just fixed my heat problems today with a used HVAC control unit I picked up on E-Bay. But doesn't your car use the standard blend air flap to control heat and cool operation as well so even if your monovalve is full open that the blend air flaps would open to suck in cooler outside air to mix with the heater core air? That is what mine does and all other cars I have ever seen..... Mine now works perfect and operates the Aux pump and Heater Valve as it is supposed to. My old unit would not close my heat valve and would not power my aux pump properly.

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~Jamie
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2003 Pewter C230K SC C1, C4, C5, C7, heated seats, CD Changer, and 6 Speed. ContiExtremes on the C7's.

1986 190E 2.3 Black, Auto, Mods to come soon.....