Can anybody explain why this works?

Both overclocked heat vents pull in the max amount of heat they can get, so 36 per second. 40 of it is cooled by the 2 vents themselves and the 3 components have 6 sides touching components heat vents (4 heat per side, so 4*6) for a total of 24 cooling. 36*2-20*2-6*4=8. This is where the exchanger comes into the heat game. It gets the 8 heat left and pumps it into the hull. Because there was already a lot of heat in the hull, the heat doesn't go into the second overclocked heat vent as it was already satisfied with 36 heat. This 8 heat gets vented out by the other components. I hope you can see that the design itself isn't very good, but it helps to explain certain behavior. This is a little bit cheaper, still not perfect.

Oke, but what is the problem with understanding this? All four vents have a cooling power of 24 (itself + 1 side touching the component heat vent) and the 1 (middle top) pulls in 36 (-24 from cooling) and the 12 excess is redistributed by the exchangers to the others 3 vents. And that's how all 4 of them work. The exchangers move the heat to where it can be vented out, 36 per second.

Overclocked heat vents pull in more heat then they can vent out. So if you need to cool 40 heat and you want to use 2 overclocked heat vents, the first vent will pull in 36 of the 40 heat and cool only 20. The other vent would like to pull in 36 heat, but there is only 4 left in the hull. This means the first vent will pull in 16 heat too much every second until it gets more than 1000 and is destroyed while the other vent doesn't heat up at all. That is why you use heat exchangers to remove heat from the first component (the 16 extra it pulls in) and put it in the other vent which will pull in the 4 and gets 16 added to it for a total of 20. So you basically have 3 options for the overclocked heat vents. 1. surround them with 4 component heat vents so that the cooling power goes to 36 which is what it pulls in. 2. use exchangers to pull the heat out of one component and put it in another. 3. use exchangers to pull heat out of the vent and put it back in the hull. Hope it helps.

The code start checking like people read. From top left to top right, then the next line and the next all the way to the bottom. When it comes across heat vents it tries to pull heat out of the hull, but if there isn't any it won't do anything with the vent that cycle (or reactor tick, second). When it comes across exchangers it tries to balance the heat between the components, or the components and the hull if it is capable of doing so.