I would like any comments on diagnosing an issue with a manual A/C controller for a 1978 NYer. The doors for the ventilation are in the "Vent" mode regardless of the button you select. The temperature setting is working as are all the speeds for the blower, so that should cancel any electrical issues. I am getting a strong vacuum at the end of the hose-line from the engine. I no longer hear any sounds like any of the doors are operating. Is it common for the white colored plastic five push button switch block to degrade and crack resulting in a leak so none of the ventilation door actuators stop working? I have heard a vacuum leakage sound from the automatic parking brake release when it operates. Does the ventilation and the parking brake use the same vac lines? Is it a concern - possibility? Everything worked in all mode when I took it out last. Every month I run the car and cycle through all the ventilation options to keep everything working.Any comments on experiences with this would be appreciated.