I have a 410a system installed 6 months ago and called for a PM since it is getting warm in Southern California. Furnace checked out just fine, filters are clean. Tech was checking charge on my Lennox HSX 19, stated on paper "by approach method temp split is 18degrees" but tech told me that pressure split was not right. He said it might be from contamination or a kink in the line. So he recommended to recover, and pump down unit and re-charge with new refrigerant and check pressures again. Does this sound like a reasonable plan? Should filter-drier also be replaced? I would appreciate your guidance.