I was called to a home to perform preventative maintenance on a Trane AC system. The homeowner had noticed that the AC wasn't cooling the house as well as it used to, and they wanted to make sure that it was running efficiently. I started by checking the refrigerant levels and found that they were low. I added more refrigerant and tested the system again, and the AC started cooling the house more effectively. I also checked the air filters and found that they were dirty, so I replaced them with new ones. This helped improve the air quality in the house. Finally, I checked the electrical connections and made sure that everything was working properly. Overall, the preventative maintenance on the Trane AC system was successful, and the homeowner was happy with the results.