Arrived to do a dual system performance maintenance. Set up for combustion analysis temperature split and static pressure tests for each system. Verified operation of all mechanical and electronic components of each furnace. Checked blowers for cleanliness and to see if there is any play in the bearings. Found that the fan in each system is coated in dust debris. Checked each systems heat exchanger to ensure proper venting of flue gas. Performed an electronic gas leak search. Both furnaces are operational at this time.