Can fully bottom grill block in 60F weather.

One of the first things I did when I received my Prius about a year ago, was to install a sheet of cardboard ahead of the radiator. There is a structural member there that keeps the cardboard several inches away from the radiator. It required me to remove a top panel to be able to access the space. I left it in place all year, with temperatures up to 30C, and I didn't notice any decrease in fuel economy, but it certainly made it more comfortable inside during cold weather.

 

Your AC must struggle. You’ve covered it’s heat dissipating radiator (aka condenser). Not to mention the engine/inverter radiators. I can see a partial block in winter, but this doesn’t make sense.

Anyway, I’ve said my piece, letting go.

 

You may have a point; I run my A/C in ECO mode most of the time, which I believe is 50% of normal.
There was a hot spell last summer when it seemed to be inadequate, so I created a custom driving mode profile, which had all the same settings as ECO, except it ran the A/C at full capacity. I only had to use that setting a few times.

 

Wait a minute,
What if the user doesn’t use AC at all?! I block 100% on lower grill during summer morning errands and don’t run AC.

 

If I wanted to overthink it, I'd have probably taken the cardboard out, but I saw no problems from leaving it in.

 

I thought all Gen 4 and newer Prius had active grille shutters. Were they removed from later models?