Cooling option will not be available in multiplayer. I tried, but it is impossible. If you are a modder and are interested in the details here is what I can read from the decompiled java code

There is a function in that calculates a temperature for a given square on the map. That function takes into account many variables, for example global temperature, sunlight depending on the season, indoors/outdoors, also if that square is a ground floor or not. It was kinda interesting how many small details game developers took into account, really nice work. After calculation, there is check if there is an extra source of heat. If that heat is greater than the previously calculated temperature, it becomes the actual temperature for the square. So if the heat source value is smaller than the normal temperature for the square, it is discarded. That is why cooling never works. The exception is when player is in a vehicle, then temperature is taken from the passenger compartment and has nothing to do with anything else. I tried creating a virtual vehicle that player would be in all the time, but it doesn't work, player freezes in car seating position without a car :) So the only option was to manipulate the global temperature for the world. In single player, when player is inside a room and a heat source is detected, I lower the global temperature of the whole world so it matches the ac setting. Since it is a single player game, there is no way other players standing outside would report the kinda cheat that I'm doing. But there is a risk that something may break, for example there are mods that would kill your harvest when temperature is too low, but that is below 5C, so 10C+ should be ok. In multiplier only server can control climate, that means I can change temperature locally for a player temperature, but it will be overwritten by the server synchronization packet every 10 game minutes.