We have a tri-level house where the middle (which is our living room) is the in-between level. When we turn on our A/C we find the downstairs to get pretty cold but the upstairs not so much. So, we've turned down the A/C further so it stays on and the upper level gets colder. We live in Southern California and we have pretty good sun exposure - especially the upper level (temps in the summer months can hit 100+). In the past we've closed the vents downstairs and had most of the air upstairs, but we were told not to do this from an AC expert that was there to look at something else. He said that we get good flow and that our A/C unit is performing well. BTW our thermostat is downstairs.

So, what can we do to get cold air both upstairs and downstairs? Should we not listen to this "expert" and close the downstairs vents or is he right and we need to find alternate solutions. Really, the idea of having the AC on longer is fine except that it gets pretty chilly downstairs and it's still only a little cooler upstairs so that is comformtable as well.

I would just keep closing the downstairs vents. As long as the unit is getting enough air flow to keep the evap coil from freezing, closing the downstairs vents won't create any issues. Also, I would suggest relocating the thermostat to to mid or upstairs level (mid would be ideal), but downstairs is fine, just have to learn to set it where it makes the rest of the home comfy. Over all, simply closing down the downstairs vents is the easiest solution. If it has worked in previous years, it will work for future years. Also, keeping blinds, shades, or curtains closed in the mid and upstairs portion of the home will help the cooling process overall. Even with the downstairs vents closed, the basement will stay cool, as cool air falls. Are there any return grills in the basement?

Thanks for the reply - the bottom floor is not a basement - it's our kitchen, dining room and entrance area. As you mentioned, we were told not to close the downstairs' vents because of the coil freezing. But you think that's not an issue? How would we know if we are at risk for that happening?

Any time you start shuting off registers its bad on your system. The system has to move X amount of air (cfm) per ton. When you restrict air flow the amp draw on your compressor and blower motor jump costing you more money to operate and making the parts fail. Have you ever checked in to zoning?

T-Top. Zoning simply shuts down a portion of the ductwork which is basically the same as shutting down vents, yes? All depends on how the system and ductwork was sized, if there are enough supplies on the upper floors, shutting down a few on the lower floor won't make any real noticeable difference on the equiptment. Just need to make sure there is enough cfm across the evap coil with the lower vents closed. This is the reason supply registers have manual dampers in them, to evenly heat and cool areas, right? I agree you don't want to close down too many, but you can certainly close a few or at least shut them down enough to slow the flow, just make sure all the upper level vents are completely open.