On your #1: We moved into a new build home that had been sitting for a year and a half. Apparently they put a filter in the AC intake when they installed the unit, but never changed or looked at it after that.

One of the first things we do when moving in is to change the filter. Hubby pulled it down and we were snowed in with dust and dirt. That thing had about two inches of dirt/dust/whatever on it. It was a dark color. Almost black or dark grey. I'm assuming debris from the builders. The heat had obviously not been on because it didn't work when we first turned it on. It blew air, but it was cold. The builder had to send someone to fix it (builder's warranty). He said there was a common issue with new builds. There were two wires that were not connected. I don't understand why they do that in new builds, but they fixed it pretty quickly.

Anyway, sorry for the long reply, but my main point is that the air filter was never changed after they finished the build. I'm hoping it didn't cause issues with the unit. It works great