The heating system has ammonia in one of its loops, which is very irritating to human eyes, nose, throat, and lungs. On Earth, you can just leave spilled ammonia for a few hours, and it will waft away into the atmosphere until it's at a low enough concentration to be tolerable. In a space habitat, it would be terrible. You might be able to get everyone into space suits, evacuate the atmosphere, and refill the atmosphere. However, the ammonia would seep into fabric and plastic and be difficult to completely exhaust.
Ammonia is a good refrigerant, and it's still usable below the freezing temperature of water, which is why they tolerate it on the ISS. The 2019 news about neopentyl glycol being a viable solid refrigerant is great... if it's usable as a refrigerant at both cold and human-range temperatures, then spacecraft cooling can be made safer and more reliable.