Performed customer 3 system hvac inspection There are 4 units one has been disabled due to gas leak. Changed qty 10 (20x20x1) system filters Checked over all operations for upstairs system on left hand side this is unit #1. Gas furnace is 20 (2005) years old. Cleaned pressure switch tube, cleaned flame sensor, Amos for inducer draft motor tested good with no issues, blower motor Amos tested good with no issues. Advised customer of dirty blower wheel and no flood protection for drain line, customer approved to have installed today, customer approved blower wheel cleaning. Made sure all connections were tight inside furnace control board. Checked heat side of system only today. Evaporator coil is very rusted. Recommended updating aged system, customer declined recommendations at this time. System is heating at this time. Did full evaluation for unit #2 downstairs on the left. Gas furnace is. 20 (2005) years old. Checked over all operations of system, cleaned flame sensor and pressure swi