If you gut the monovalve it becomes a monotube and allows flow, which eliminates it as a source of trouble for "no heat".

Where I live, there is a distinct heating season, and a much shorter A/C season. So gutting my monovalve would be OK in the heating season. And it would make my Benz equivalent to my Subaru system which has no such heat control valve, resulting in heat flowing through its heater core all the time. The Subaru climate box simply tries to steer air through either the A/C chiller or the heater core in proportions to mix the temp. Which is stupid in the A/C season because it takes a certain amount of A/C just to overcome the heat and break even. "Fresh air" blows warm in that car because it must pass through the box with the heater core in it. I wish the Subaru had a monovalve, but a pair of vise grips and a rag clamped down on the heater core hose would also do I suppose.

Anyway, if my monovalve ever failed and I didn't have a working spare, I'd be inclined to replace it with a pex fitting ball valve from the plumbing shop. Open and close the ball according to season.

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Cheers!
Scott McPhee

1987 300D