If the senario is as I stated and you are having problems in the middle button position, then you have either a vacuum problem that keeps the mode door open or the mode door potentiometer is broke or misadjusted. Dealing with the mode door or potentiometer will require a technician or a lot of research.

Here in Florida its easy, just use the top,"Max AC" button, who needs mixed temperatures, we just go for the cold.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician