They are easy to install. As far as it will not turn on or off wothout you turning it,......? Take the front cover off. It just pops off. Thats if you have a T87-f gold round t-stat. sounds like the mercury bulb is stuck due to the cover being on too tightly. Try this and let us know what happens.

Hi Hollywood,
Thank you for your reply. My husband took the cover off and dusted the cob webs off of it. Its exactly the one you described. After he did that it began working again. In the meantime we purchased a digital thermostat and hope this will solve our problem The other one was always at least 5 degrees off. Another thing--it will work a few days and then I will notice it's not shutting off again. This is why we bought the digital as they said it was the best to use. Any advice on that? Thank you,Debbie C.

Digital setback t-stats are nice. Can save you money. As far as the unit staying on at times, the contactor in the outside unit may be sticking. If so it must be replaced. This will require a service tech.