Bart, what I notice is that as soon as the camera has power and gets connected to a computer, the fans start working. But it doesn't start cooling until I start Ekos. That's why I assumed that Ekos was activating the cooling of the camera.
There is an easy way to check this. Connect the ASI1600 to your pc/laptop/SBC/RPi/WhatEver, start Ekos and wait until the camera has cooled down. Then stop Ekos but leave everything connected. Note that the fans don't stop. Start Ekos again after 2 minutes and you should see that the temperature of the camera is high and going down again.
It actually does cool, though not controlled. But you can see that the 12V draws some power (0.3-0.4 Amps IIRC), and the temperature goes down. I.e., if I connect it with ambient temperature of +5 degrees, then leave it like that for a while, and then connect the INDI driver, the temperature will be well below zero....
My 1600MM-Pro also starts cooling as soon as I start INDI. It does now, I have to say. It didn't do it a year ago. I cannot say when exactly it started. I had assumed I had clicked 'save' with active cooling at some point. But if that doesn't store those settings - maybe it was after one of the upgrades of the asilib? So it could be the newer SDK driver doing this?