Thx Benz Mondi. I disassembled and inspected the monovalve itself. No short in the solenoid. Spring action good. Everything was spotless. No build up. No tears in the diaphragm. Movement was smooth. Bench tested, cleaned, and reinstalled. The monovalve works as it should when it sees 12v (i.e. it closes and A/C side vents blow COLD), but the monovalve just never sees a ground path from the climate control unit (i.e. no triggered ground).