On Approx. 30% of my calls, the H.O. has all or nearly all of the first floor registers closed in order to move more air to the second floor ; it doesnt work , and more importantly, it will almost always return liquid freon back to the Compressor in the A/C Unit ... which is designed to pump vapor only. Damage can and often results. The reason liquid gets returned is due to the air not flowing fast enough over the Cooling Coil to evaporate all the liquid freon when you have a bunch of registers closed . Nearly all duct systems in residences are undersized/poorly designed, and closing down registers only makes the system more choked down. Just want to give you a heads up as this is a very popular thing H.O.'s do without realizing the ramifications.