Performed a heating pm on a gas furnace. Checked the air filter- customer replaced. Blew out drain line. Started and checked the safeties. Performed a combustion test. System is operating properly. Performed an A/C pm on the system. Checked the condensate pump. Rinsed the condenser coil. Checked the electrical connections, pressures and temperatures. System is operating properly. The system is older. Recommend replacing in the future. The neutralizer stones need to be replaced.