Try feeling the hoses on both the upstream and downstream side of the monovalve.

If you are feeling a "cool" hose downstream after engine comes up to temp, I'd bet the monovalve is closing.

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles

Well, folks, thanks again for all your help. I replaced the button control unit this evening, and used some steel wool on the monovalve connection posts. At the same time, I replaced all my burned out light bulbs, and it is nice to be able to see the AC controls again! I never could have done it without your help, and I'll let you know if this fixes my intermittent AC issues!

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1983 300D (Hans)