Ductwork pinging or popping. If you listen to a pinging or popping sound coming from steel ductwork, This can be due to thermal enlargement or by air blowing earlier a unfastened flap of steel. Make sure all wires securely connect to their terminals and that the duvet received’t pinch them. http://acrepair08395.blogprodesign.com/19435387/the-basic-principles-of-ac-installation-contractor