Have a 95' C220 with 4 cyclinder gas. When weather is hot, AC and blower change with acceleration. The system only works like it should when cruising at a constant RPM down the road. Seems to be vacuum related as the air from changes from the front vents to the defrost vents when accelerating and back to normal when you let off the pedal. I've checked all accessbile vacuum hoses. Are there diaphrams and other vacuum related control devices under the dash? Please help, wife is forcing me to sell if I can't fix it!