Chevrolet Repair: 95 blazer, engine surge w/ AC on, vents close, 4x4 blazer, vacuum line

Question
My 95 4.3L 4x4 Blazer's engine surges only when the AC is on AND not idling.  The vents also close when this happens.  So basically AC only works when parked.  At highway speeds the w/ the AC on, the periodic surge drops the the revs by about 500-1000 rpm - this is a lot, so we can't use it.  We have had carbon build-up issues w/ the EGR, but I have cleaned it and it appears to be working fine (these symptoms are much different).  The AC system alos has intermittent issues w/ not switching between zones (e.g., defrost vents to upper panel vents.  I'm guessing it is a check valve to the intake manifold or something like that.  Any ideas?

Please let me know where the parts on the engine are located if you have a solution.

I asked Van this question also.

Answer
Without actually putting gages on the AC system to see what the pressures are doing there are numerous possibilities.

The vent problems are most likely due to a vacuum line leak somewhere on the engine or under the dash.


What mechanical work or ANY kind of work has been performed on the vehicle recently ?. As most problems that occur after a recent repair was made can be traced back to the area of where the repair was made as an electrical and or vacuum line may have been knocked loose. Look around in the area where work was performed..