HVAC installation mysteries
No matter how well you think you are prepared, there is almost no way to ensure you won't have a problem with your heating and cooling unit installation without professional help. Have you home inspected even if it’s in a city where inspections are required. Most of the photos you see here are within the city limits.
Most problems are obvious, they just don’t make sense. Call the builder, see if he concurs. They should take it from there. If in doubt call an independent inspector and ensure they have experience in HVAC inspections.
All else fails call the BBB. Hopefully it won't come to this, but remember that avenues like small claims court are there to protect you from unscrupulous contractors. The information provided by an experienced inspector can help ensure success if you do need to resort to extreme measures.