ᐅ Outdoor unit of air-to-water heat pump is smoking and steaming

Hello everyone. Our air-to-water heat pump has been in use for about half a year now. We recently noticed some hissing noises coming from the outdoor unit. It sounds similar to a truck brake losing pressure, but somewhat quieter. I have heard this noise three times so far. The last time, I happened to be outside near the outdoor unit. The noise appeared, and the fan stopped running—not suddenly, but gradually. I stood right in front of the unit to see what was happening. After a few seconds, the fan turned on again. At that moment, a kind of "cloud" appeared. Not a real cloud, more like when you blow dust off an old book. It didn’t smell like something burning, but more like intense heat being generated. I hope you understand what I mean. How would you assess this situation? So far, neither the heating system nor the unit has shown any error messages. The heating is working perfectly. Because of the weather, the outdoor unit is practically running almost non-stop. Could this be some kind of overheating that causes the fan to briefly switch off?

I believe the systems defrost from time to time at temperatures below zero. That should be normal.

This is the defrost program.

That is certainly possible; I hadn’t considered that. Although the temperatures are still just above freezing, the system’s operation could definitely cause icing. To check this precisely, I would probably need to inspect the water outlet on the unit in this situation, right?

No water escapes from these devices. They just get very cold so that the inside can stay warm (basically a reversed refrigerator). Moisture from the air then freezes on them. This ice has to be evaporated again using a lot of energy so that air can pass through the fins.

I was walking my dog earlier in a new housing development. Little clouds were coming from various plots. It seems quite ridiculous that expensive electricity is also needed to heat the fins, only for them to then do the exact opposite to heat the house. Besides the fact that it looks pretty silly, I just can’t warm up to these things (haha).

Yeah, that’s normal. Especially around 0 degrees Celsius (32°F), the air is extremely humid, and the components ice up a lot. When it’s dry and cold, like minus 10 degrees Celsius (14°F), this doesn’t happen as often. And certainly not at temperatures well above freezing.

I was pretty shocked the first time too 😀