Arrived to do a performance maintenance. Set system for cooling. Measured the systems static pressure and measured a temperature split between return and supply air. Found that the system is operating with failing static pressure. Checked interior of the furnace for cleanliness. Found that the blower wheel is starting to collect dust debris. Found that the evaporator coil is impacted with dust debris. Went outside and verified refrigerant levels. Verified operation of all electronic and mechanical components. Rinsed coil free of debris. Spoke with homeowner about the system. Recommend using filters with a filtration rating of merv 8 or lower. Filter is 20x30x1. Should probably be changed every 2 months. Air conditioning system is operational at this time.