Returns on split system

Are both returns on a split system always used or does it pull from one or the other depending on heating or cool one of the zones?

I have a 5 ton unit but the air handler/furnace has a diverter on there because I dont think the returns are big enough. There are two returns one is 14" round the other is 14x20.

Im thinking I need to get some professionals in here and have them add more returns from a couple of the larger rooms.

submitted by /u/Liberte1911
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