Donald Snook wrote: > I took a trip 300 mile trip the other day in my 1990 300SEL (128K) and I > noticed that when I was climbing a long steep hill (steep for Kansas, > not steep for anywhere else) my a/c would stop blowing very hard. It > was a very hot day and when the a/c would stop blowing it was > noticeable. When I crested the hills and proceeded down the hill the > a/c would return full blast. This was all at 75-85 mph. Could this be > a vacuum problem?
Probably a minor vacuum leak. At large throttle openings manifold vacuum drops to almost nil. To allow the HVAC system to still function properly, there's generally a reservoir somewhere and a check valve to provide a steady vacuum source. If the check valve is bad or there's a leak somewhere, the vacuum will bleed down to nothing when you have your foot in it for a long stretch, and the HVAC flaps will go to their 'default' positions.
