Room Air Conditioners…

My mom has heart problems and needs the AC to be around the mid-sixties. We recently moved into an older house, and the air conditioner is polar when it comes to doing what it is expected to. It randomly stops being cold, and sometimes freezes up. I think we are putting more pressure on it than any other owner previously. It is in the eighties now, and I would just like some tips to make it work a bit better and more efficiently without the high cost of bringing a technician in.