Performed maintenance on 23 year old Lennox furnace. Furnace is single stage unit with 2 zones. We are only servicing the unit above the right hand side closet next to the office. Does not want other unit serviced. Cycled system for heat. Verified proper heating sequence of operations. Temperature rise across heat exchanger is in range when both zones are activated, but is slightly high whenever one zoned is closed. Amp draws on indoor blower motor are high but within range. Secondary motor control was recently replaced and is in range. Blower wheel is slightly dirty. Checked heating components. Cleaned flame sensor. Cleaned blower assembly and heating compartment. Also wiped down unit exterior. Flushed out condensation lines with cartridge. Replaced 1 inch filters. Pulled blower assembly and inspected heat exchanger. Heat exchanger doe have some hot spots, but Areas of concern were inspected and all checked good as of now. Homeowner has 1 visit left for cooling. Cycled system, system