I was called to a home to perform maintenance on a Trane air conditioner. The unit was not cooling properly, so I checked the thermostat and found that it was set to "heat." I reset the thermostat and tested the unit again, and it was cooling properly. I also checked the air filter and found that it was dirty, so I replaced it with a new one. After completing the maintenance, the customer was happy with the results and thanked me for my help.