I was called to a home in the suburbs to inspect a Lennox AC system that was not cooling. Upon arrival, I found that the system was not producing any cool air. I checked the thermostat and found that it was set to the correct temperature. I checked the air filter and found that it was dirty, so I replaced it with a new one. After replacing the air filter, the system started cooling again. I also checked the refrigerant levels and found that they were low, so I added more refrigerant to the system. After completing the repairs, the customer was happy with the results and paid me for the service.