What is the best setting for two air-conditioners?

Factual Questions
1

The background: We moved into a home that is two stories tall with a central air conditioner (actually a heat pump) for downstairs and a second central A/C (also a H/P) for upstairs. We are beginning our first summer in this house. At night, the tempurature gets down to the mid 70’s (F) this time of year. In several weeks, the temp will stay in the high 80’s all night.

The problem: At night, I turn the thermostat on the downstairs unit up to around 85 degrees. All the bedrooms are upstairs, so I figure there is no need to run the A/C when no one is around. I set the upstairs unit at a temperature we’re comfortable with and we all go to bed. Often, around 4:00AM or so, my wife or I will wake up because of uncomfortable heat. We usually lower the upstairs thermostat and go back to bed. Another detail: the door to the master bedroom where we sleep is right next to the top of the stairs.

The question: What is the optimal way (in both comfort and economy) to set the thermostats in this situation? Am I better of leaving the downstairs area cool all night, even though no one is there? I suspect that, since heat rises, the downstairs warms the upstairs area and the upstairs unit has trouble keeping up.

So what do y’all think? Thanks for your attention.

2

It really depends on the setup.

Basically you would like to cool the rooms you are in and not cool the rooms you are not in.

perhaps it would be better to move the up/s thermostat to your bedroom this way the temp it reacts to would be where you want it to.

you should consider a programable thermostat this way you can set a time for one to cut back and the other to come on.

Assuming you use the down/s only when you are not sleeping the up/s only when you are sleeping I might set a programable thermostat this way:

1 hr before bed the up/s thermostat sets to coldest setting (not the coldest but the coldest you would want it) - and to the warmest setting (or off) at the time you leave the bedroom. If you have another set point I might start some up/s cooling 2 hrs before bed.
the downstairs i might set up like:

1 hr before waking it goes to the coldest setting then have it turn off (or low) when you leave for work, turn back on to coldest 1 hr before you return then off at bed time.