air flow for AC and heat is normal until I hit 2000 RPM,then fan still blowes but no air comes out, unless I drop below 2k RPMs. I suspect vac. line but can't locate any info on their location, except info on vac. line to transmission for shifting, which the shifting is fine, so they are not connected. Went to Auto Zone but their book showed no info for the vac. system. Can anyone help me?