Performed fau Maint on 6 year old Lennox 98% furnace. Cycled furnace for heat. Verified proper heating sequence of operations. Temperature rise across heat exchanger is high, and system was going off on high pressure. After inspecting unit, found a very dirty Merv 16 filter and very dirty 1 inch filter which was restricting system of airflow. Removed 1 inch filter from return cabinet, and replaced Merv 16 filter with filter provided by homeowner. Cycled system and system ran with no problems. Amp draws are normal. Blower wheel and Evap coil are clean. Tested and verified safety components. Wiped down heating compartment. System is not surge protected. Cycled system, system is operational upon departure.