Last fall we installed a new heat/central air unit. Heat (NY) ran all winter and the unit was excellent. This summer for 1st time we ran the air. The smell is over powering throughout the entire 1200 sq ft house (one floor plus basement). Installer was called and he put a trap on the condensate lineand my husband taped in the filter. We have a dehumidifier running. The smell is like gas. We have a septic system. I walk in house (probably have tried it 5 times now) after it runs for a few house and every inch of the house smells to the point where air has to be shut down and every window opened. I have put every buzz word into the internet and asked my husband (could this be the problem) on everything I read. Husband built home so he does know construction type things. He has a smell issue but 2 friends just opened up door and could smell it the other day. Please help it's hot here and I can't run the ac.