My baby will also have blocked nose or difficulty breathing when she sleeps at night in our air con room. But she learned to breathe through her mouth if she wakes up. Previously when she had flu, I would spray Sterimar and leave it on for a while then use a manual nasal spray to suck the mucus out. Will do it few times a day whether or not there’s mucus. I would also gently clean her nose using a cotton bud every morning. If all else fails, you can do doc and they will prescribe you with iliadin to be dropped into baby’s nose once at night.
Maybe try sleeping without aircon? U have to trial n error n see whats working best for the bby.. maybe he/she is very sensitive to cold.. as for the sterimar think u r doing it right