Exit temperature of the air coming from the AC is 16°C but room temperature only reaches 22-23°C (about the same as outside temperature of 22-24°C) after running all night long ?
Based on this description I would suggest you close the doors and windows and try again
Seriously, it does sound like the unit is working but there is too much heat entering the room. There can be many reasons for this and typically it is a combination of things:
- poor insulation of outside walls
- single pane windows
- air leaks to/from exterior
(those first three you don't normally expect in a Montreal home but who knows)
- open interior doors (a room air conditioner will not be able cool your entire house!)
- air flow through heating ducts
- room below too hot (heat rises and even with ceiling insulation you will get nice warm floor)
- forget to turn off heaters (forced air heating would be obvious but baseboard electric heaters can be easily missed)
To keep the performance of the room AC at maximum ensure that the filters are clean and replace them frequently (since the unit is running non-stop they may need replacement more often) and that the coils are dust free.