air conditioner turned off is:
and (oversimplifying) that when the airconditioner is on that:
The essential assumption is that the air conditioner removes heat at a constant rate,
while heat flows into the room at a rate proportional to the temprature difference.
The problem is that the thermal capacity and heat loss constant for a room
are difficult things to calculate. There are tools to do so but I doubt you
will want to look for them.