We ran a no A/C warranty call today on a 6 month old Trane 410a system that we installed. The tech found that a rat had actually chewed a hole through the aluminum tubing on the condenser. This bionic rat was no where to be seen just a nest and teeth marks all over the tubing. This wasn't just a small hole but a big gapping hole, indicating that after getting blasted in the face with freon he actually came back for more!
I have experienced first hand the damage that one rat can do. But chewing through metal is a first. I would hate to have this rat lurking around my house.