HVAC: Don’t shut your air vents to give you better heating or cooling in certain rooms/floors. You’re adding pressure to your system and reducing its life. If it’s AC then you’re turning it into a freezer. That’s why doing so freezes the coil, not enough air flow to move the cold air out and keep it from freezing. For heat it literally can overheat the control board frying it since the blower also helps cool the electronics. If you have hot and/or cold rooms (this is normal per floors) ask about adding dampers. Most of the time it’s not possible without major drywall rework and it isn’t cheap. Your builder sucks (basically). A lot of companies won’t quote the work because it can’t be guaranteed. You’re essentially stuck with the crappy design the builder got approved. One potential is minisplits. Again, not cheap per room and not pretty but they will fix your issue.