It is cycled on and off by the CCU to regulate the heat when the temperature gets close to the temp set on the wheel. If the temp in the car is lower than the temp set on the wheel the monovalve will be energized. If the temp in the car is higher than the temp set on the wheel, then the monovalve is not energized. If the temp in the car is the same or close to the temp set on the wheel the monovalve will cycle on and off.

Paul

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84 500 SEL (307,xxx miles)