How to switch between two central air conditioners so only one operates at a time to reduce peak load.?

Question

How to switch between two central air conditioners so only one operates at a time to reduce peak load.?

Answer 1

The only reason I can think of that you'd want to do this is you are out of headroom on your main electrical panel and so now you can't run both units at the same time.

But the problem is that A/C units need to be controlled by thermostats that can call for cooling whenever it is required and modern thermostats have programs that monitor how long it takes to reach a given temperature and those programs help to save energy, so if you jury-rig some kind of time-based cut-off for each unit, you are going to get uneven cooling in both zones and waste energy which just replaces one problem with another one.  

So what you need to do is fix the underlying problem, your current panel cannot handle the peak load of both systems.  You do that by either upping the size of your main panel ($$$) or having a new sub-panel installed to power one of the units.  We had central air retrofitted into an older home with a maxed out, 120Amp breaker box from the 1970's.  The installer just tied into the main supply line before the box and then put a small breaker box with time-delay fuses outside near the connection point.  So you don't have to up the size of the main box to get the headroom you need.

Fooling around with the main supply wires into the house can kill you, so this is not a do-it-yourself project.  You need a professional electrician to do this work, but you can fix this the right way without dropping the big bucks on a new 200Amp service.

Answer 2

Get a multistage thermostats, it's designed for low-voltage operation.