Hi there is still some small bug with the air condition.
I used a train with some "xmz" and WRmz wagons. There were some Bmz which are all 100 the same. The temperature outside was 25°. I activated the CZE and the AC worked fine and cool down to about 18-22°.
After about 1 hour of drive the ouside temperature decrease to 24 and later to 23. Then the AC in one Bmz 0-12 didnt work anymore. The wagon temperature was always 24 and 23 and it doesnt show "acitvated" anymore. I tried to put it off and on again and also put of the CZE but it didnt work again. After a while later the same happend to two other wagons. All the other 100% the same wagons work correct.
It must have to do something with the outside and inside temperature. Maybe the script which decides if the AC should be turned on or not.
That's completely normal. In Open Rails, the AC/heating has certain threshold temperatures set, which turn the AC/heating on or off. It's like a thermostat in house's central heating system.
Here are more thorough explanations:
In case of the heating, the lower temperature threshold turns the heating on. As the temperature inside the wagon raises, it'll reach the higher temperature threshold, which turns the heating off. After the temperature in the wagon drops back down, the cycle repeats.
In case of the AC, the higher temperature threshold turns the AC on. As the temperature in the wagon drops, it'll reach lower temperature threshold, which turns the AC off. After the temperature in the wagon raises back up, the cycle repeats.
In your case, it looks like the AC reached the lower temperature threshold and turned itself off, but due to outside temperature, the temperature inside the wagon didn't reach the higher temperature threshold, so the AC remained off.
Also, CZE (Centrální zdroj energie) or in English "Central power supply" works completely independently on heating/AC. The only disadvantage is, you can't see, if it's working or not from inside the loco. Well, unless you're driving ČD class 754 (Goggles wearer) with the original cabin, where you can see some amperage on heating circuitry ammeter, even when the heating/AC in the wagons is turned off completely via F9 menu (that's CZE, drawing power from heating circuitry).
Also a few notes:
1st: The temperature thresholds for heating/AC seems to be chosen randomly. IRL, the train driver doesn't set the wagon's thermostat, this is usualy done by another crew member (mostly by train's conductor, but it can be someone else from the train's crew). Sometimes these values are really bizarre, for example in one simulation, one of my wagon's heating reached 26 °C before it turned itself off. And in one simulation, one of wagon's AC reached 17 °C before it turned itself off.
2nd: These temperature's thresholds are only present on AC, electric heating and diesel heater. Steam heating and solid fuel stove heating don't have those thresholds (obviously). In case of steam heating, if the temperature inside the wagons is too high, you have to either reduce the steam output to the heating or cut out steam heating completely.