Hi guy's I have a 00' ML320 and the heater/windshield defroster doesn't want to work. All fuses -the relay (MB already replaced) with new one, engine water is hot, blower motor works fine. Regardless of climate settings, blower settings, air coming out of vents is either ambient or super cold. Is there an interlock that can be preventing this from activating? I know some other MB models have a ac/heat control valve in the engine compartment. Is this possibly the same problem? Can't afford to leave my only vehicle at MB for a day or two to have them inspect it. I suspect my vehicle has this valve and it is stuck. Does anyone know the location of this control valve? Thanks for any help.