Air conditioning+baby= always sick :(?

I use to keep my air on 75 but ever since I had my girls I keep it on 77-78. During the day my 20m old is fine. No cough or boogies. But EVERY morning she wakes up soooooo congested (chest) she goes to sleep with socks, pants, and long sleeve pjs and I cover her with her blanket but she does not like it and ALWAYS kicks it off n she tends to sweat a lot just like her dad (even when its cold) now my question is why does she wake up congested every morning and gets sick at night? 77 isn't too low. I'm getting tired of it bc she's always getting sick and well I blame the air bc its at night. The air vent throws the air in every part of the room so I can't move her bed and I cover her but she takes it off. Even after she falls asleep n it I put the air higher its too hot. I don't think 77 is too cold. I don't use covers either and if I do its the thin sheets and just to cover myself so people won't see me in pjs.