Have a two story home with one system on each level. Each system has an ecobee thermostat and one sensor. Over the past week, downstairs is running about 3 hours more per day than the upstairs. This is the opposite of what I would expect. Any idea why this is happening?

Upstairs AC set to 79.
Downstairs set to 77.
Both set to run 15 mins minimum to prevent short cycling.

Same setup as you, but my upstairs runs hotter and cools more as expected.

Is your downstairs temp figuring in additional smart sensors? Just curious. NM see you have 1 additional sensor. Hmmm.

Is the upstairs used as much as down? Is eco mode enabled upstairs? If there is less activity it might be trying to save you money by auto adjusting the temps and running less upstairs.

That seems oldd but that 2 degree difference could be a part of it. Have you considered setting them the same for a day or two and compare? Logic would tell you that upstairs runs longer all else equal...

Change your filters and clean you condenser coils would be a good place to start. Check on your evaporator coil as well. If those are dirty they would make your unit work harder than it should.

Thanks all.

We use the upstairs less often, but I disabled ecomode for this reason. Ecomode is also disabled downstairs.

Changed the filter today. Last changed the filter on 4/24. Will check the condenser coils today or tomorrow. Last serviced the coils on both units last year. Skipped it this year due to Covid.

Another data point is the downstairs system isn't running longer at any individual time, but downstairs seems to heat up quicker so it is triggering runs more often. This is particularly pronounced at night. Last night upstairs ran twice for 30 mins total from midnight to 7 am. Downstairs ran 6 times for over 1.5 hours in the same time zone.

I do have more windows (single pane) downstairs then I do upstairs.

More windows/sun exposure on 1st floor? Was it always a 2-story or was the 2nd story an add on?

Assuming the garage is attached, do you know if the downstairs interior walls which have the garage on the other side happen to be uninsulated or poorly insulated?

Garage is connected but don't know about insulation. Second story wall can be seen from the garage attic and jts insulated with pink batting.

How about door and window insulation? Is it tight downstairs?

House is definitely leaky.