My maid's room (本身係工人房) got air conditoner and she always switch on the air con without telling us.
My maid's room has a air-conditioner too. But there is no window, just a strong exhaust fan inside her bathroom.
For me, I will allow her to switch on the air-con. if it's too hot. Otherwise, she just uses fan and opens her door a little bit.
If her performance is good, I'm willing to pay a little bit extra (~$300/month) for her air-con. at nite.
My past maid does not switch on the air-cond when summer time for 2 years, she doesn't request anything, and we just gave her fan which it is enough la.
However, we will have new maid by coming end/Feb, and my kid (3 years old) will share a room with maid, my husband said will allow her to switch on air-cond because it is for my kid. Of course, Im not willing to give her, but no choice la. By the way, I will also give her a key since my kid has to go school starting this year.