Arrived in Paige for AC Tune-up, Upon my arrival I performed 6 month checkups on 3 straight cool systems. I found systems 1 & 2 are operating properly in both the performance and safety aspects. On system #3 I found that it is operating properly in the safety aspects but the performance is not where it should be. A cat had ripped the return air duct open causes it to pull in unconditioned air. This is causing the system to perform the best it can and has caused the heat transfer media coil to become dirty. I will be emailing over quotes ones I speak with my lead technician with pricing on metal duct. Quotes will include a chemical cleaning of the system and will also compare price between metal ducting and flex ducting.