Unable to turn off cold water flow in airconditioner, possibly due to solenoid valve
That's not an air conditioner at all.  It's nothing but a radiator in a fancy dress. 

The unit is designed to be supplied chilled water at 6-12°C (43-54°F) and blow it across a - well, a radiator.  It has a tray to catch condensation.  And that's about all there is to the unit. 

So it's totally dependent on external machinery supply chilled water to it, and this machinery is fairly complex. Which tells me you are in a multi-unit apartment/condo building with maintenance staff who tend to that equipment. Since this equipment is only the "head unit" for that system, and you don't control that system, you need to talk to the superintendent. They fix these things all the time and probably have spares in stock, which is good since you'd have trouble finding these at retail.