The monovalve (heating valve) is on-off. Pulse width modulation is used to control the volume of coolant moving through the heater, which in turn affects the temperature of the delivered air.

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2002 E320 T-sedan (210.282) 219K
1994 E320 (124.032) 252K (dearly departed in hit & run)
1988 260E (124.026) 301K (sold)