Though it sometimes makes sense of closing AC vents especially in those rooms where AC is not being used for quite a while. But this is not a good practice as unknowingly, you are causing more harm than actually causing good. So now it can be inferred that AC vents should remain open else the vents which remain closed can do a variety of problems few of those are listed here in this blog by AC vent cleaning service Davie for your reference.
Closed Vents Increases Energy Bills
Closing vents would result in wastage of the air conditioned air through duct leaks. The AC system works by pushing the cool air through the ductwork system and just because the vents remain closed would actually allow the cool air to get wasted through tiny leaks of the ducts. So always try to keep the vents open and allow the cool air to circulate in your home and not just get wasted.
Closed vents will make you uncomfortable
Now when the vents remain closed it increases pressure inside the ducts and that pressure also causes the blower motor of the AC unit work not too fast and result in less cool air which eventually make you uncomfortable. Now there are two types of blower motors one is PSC and the other is ECM. The PSC motors work at a certain speed and can’t cope with the extra pressure situation in the ducts and thus work slowly. The other ECM motor can adjust its speed and work well to give the required amount of the cool air but that increases the energy costs. SO in both motors, you are having a loss. So keep vents open.