From your description it sounds plausible that the dash control unit may be faulty. Try looking at that first before going for the vacum servos behind the dash (that is the long expensive job). If you eventually need to change the servos, replace them all, and also consider changing the evaporator (you don't want to go in there twice).

goog luck

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'02 C240
'00 LR Discovery
'72 280SE
'67 280SL

---past---

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'86 300E sold
'87 300SDL sold
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