I recently took mine apart and it was all messed up. If I were you, I would pull the return grate off and inspect each of the 4 lines. One of mine wasn't even connected to anything and my really long run over to the couch has 4 holes in it. Also, the runs are longer than they should be. I pulled about 4 feet of duct work out of there.
After inspection you might have other ideas on what to do or how well it works. Personally I had planned on getting the closable vents that were mentioned above.
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