Arrived to do a performance maintenance. Set system for cooling. Called office for uv bulb replacement. Measured the systems static pressure and measured a temperature split between return and supply air. Checked interior of the furnace for cleanliness. Found that the fan for heating and cooling is collecting dust. 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. Determined the debris in the ductwork is spreading to the newer furnace and air conditioner. Air conditioning system is operational at this time.