Thank you for the reply. Is the monovalve what some may refer to as a heater control valve on other vehicles? Just to be clear - the valve needs power to close, to stop the circulation of coolant into the heater core? I can try using pinch-off pliers on the heater hose to see if that helps. I am still concerned that I no longer hear the climate control unit relays clicking when turning the temp wheel. Maybe there are a couple of issues...

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1985 300D 296,000 miles - Project "Rusty" 1/4 mile in 19.9 sec @ 71mph. It's almost rust free and water proof!

2006 Dodge/Cummins 6-Speed - 670HP 1159ft/lbs