Performed comprehensive tune-up on older Lennox system. Unit in surprisingly good condition for age. Washed condenser coil, calibrated thermostat (was reading 3° off), checked refrigerant (added 8oz to reach proper subcooling). Electrical connections all tight. Replaced worn contactor showing early signs of failure - prevented potential breakdown during upcoming heat wave. System running efficiently now. Recommended budgeting for replacement within next 2-3 years as unit is approaching end of service life.