Through the years I’ve inspected quite a bit of air conditioning systems from window mounted to large capacity where several people were able to easily stand in one section and one thing is a constant – contamination. From fiberglass inside (a condition I seriously think is a bad idea) water loss, almost useless filters and dust/debris infiltration. The filter in the photo is considered by some to be almost useless in capturing small particles. This filter was also cut down to fit and not fully secured.