At what temperature should you keep your downstairs air to help cool the upstairs or does the downstairs air temperature have any effect on the upstairs if you have two central units?
I have two separate systems, one up and one down. The downstairs unit does nothing to cool the upstairs. It is probably because cold (heavy) air sinks and hot (light) air rises. To have any effect on the upstairs, you would need a very well insulated house with few windows, and you would have to make it extremely cool downstairs. Inversely, you can use your upstairs system to help cool your downstairs, for the reasons explained above. Since hot air rises, your upstairs system has a larger cooling capacity than your downstairs unit to take care of the larger demand.
