Interior fan running every time I open the door?

Hello - welcome to The forum!
When you say "interior fan"....are you referring to the air conditioning/heat fan?

I believe what you are actually referring to is the brake booster recharging the brake system.
Open the door....does the fan sound stop after about 2-3 seconds? If yes....it's the brake booster...and its normal

 

Well part of the solar roof package is to run the fan when it is unoccupied to keep the internal cabin temperature closer to ambient and not boiling hot. It is a feature you paid extra for...

 

I don't have a GenIII, so all I know about it is from reading about it. So take this information with a grain of salt.

But you should have a button to the lower left of your steering wheel with a little car and a fan symbol on it. If it is pressed in, that gives the system permission to activate as it sees fit. If it is not pushed in, it won't activate unless told to as far as I know.

But you have two features:

1. Solar Panel Ventilation System
This one uses the solar panel to power the fan to draw in outside air and vent the hot interior air. This is fully automatic (as long as you've enabled it before you turned off the car via a button to the left of the steering wheel). The fans will come on and off as needed and as power from the sun is stored (i.e. it will run intermittently if there isn't enough for a continuous run). The SPVS will continue to run even after you unlock the car and open the door. It will cancel once the car is started or turned to IG-ON.

2. Remote Air Conditioning
This is activated via the A/C button on the fob. This one starts up the A/C compressor to further cool the vehicle. The engine stays off because the compressor is powered by the hybrid battery. It will turn off after 3 mins, when the battery is low or when you open the door.

 

The A/C and the solar ventilation are two separate things. The solar ventilation can be turned off with a button below and to the left of the steering wheel. On mine, that button shows an outline of the car, a wavy arrow flowing through it, and a four-blade fan symbol in the corner. In is ON, out is OFF. And in works only when direct sunshine is on the rooftop.

 

And you have to look closely at the button to tell if it's "in" (on) or "out" (off). Once it cools off later in the year, you may notice the fan will start up, cool off the car a bit, and stop. Then, after a while it will start up again. You'll notice this if you sit in the car (car off) for 10 min or more.
I haven't noticed a great difference in interior temp with the fan running, but there must be some difference.
The fan is not very "powerful" cooling wise, but the sun IS very powerful heating wise!

 

Yeah, I remember being with a friend picking up a new Subaru and not escaping the dealer lot without what seemed like an hour of in-car instruction by the dealer.

I think you'll find the Solar Ventilation System section in your owner's manual tells you anything you want to know about it though. If it's enabled, you might notice (if you're sitting in the car for a while after turning it off) after about a minute, the slight sound of the air inlet damper moving to 'fresh' (if it was on recirc before), and then after about 10 minutes, if there's enough sunlight, the blower starting to run.

They put in the 10 minute delay so those times when you're just hopping briefly out of the car, the blower doesn't come on right away and blow away all the nice conditioned air you already had inside. After the 10 minute wait, you figure there's only hot air to be vented out anyway.

-Chap

 

On my car, the more noticeably on/off cycling is in weak sun or partial shade. That reduces the solar panel output so that sees enough voltage to start the fan, but doesn't have enough power to run it continuously.