That vacuum pressure sounds like what might be doing this....Because when it first started acting up, it seemed like the A/C and the engine were on a see-saw, and when the AC was working, the engine was idling, and when the engine was revving, the AC front vents switched to defrost...as soon as you let off the gas, the AC would switch back to the front vents...Now, after a few months, the vents take longer to come back on, usually when Im at cruising speed at 60 or 70, and let off the gas pedal....the front vents will slowly come back on....
But how do I check this? where would I find the vacuum hoses? are they inside next to the AC filter, or are they outside connected to the engine somewhere?
thanks for your help.
1998 ML 320
1994 Blue C220
Im going to Grad School @ the University of Iowa