Pressure issues

<p>I am having pressure issues with my H-Class Acquity system.  I was running a unique method yesterday for the analysis of soybean oil using IPA as one of the mobile phases and Acetonitrile as the other.  Upon switching back to my usual 0.1% Phosphoric in H20 and ACN today, the pressures have been all over the place.  In general, they are high but upon tweaking the ratios I haven't received the changes in pressures I expect.  For instance, at 100%, 0.1% Phosphoric (1.0 mL/min) the pressure was at 9000 psi.  Upon, changing to 70/30 (0.1% Phosphoric/ACN), the pressure increased---which obviously makes no sense.  At 1.0 mL/min with 100% ACN, I am getting a pressure at about 4000 psi, which seems normal to me.  Also, I did conduct a leak test and everything passes.  Any help would be appreciated.  Thanks in advance.</p>