The best setting for a window air conditioner is a temperature of between 60 F to 65 F.
On really hot days it's best to set the window AC thermostat on 60 to keep the house or room more cool as when it's 100 F or hotter it takes more energy to cool the room and remove the heat.
On less hot days a temperature of 65 F to 70 F may be good enough.
I usually keep my window AC on 60 F when at home and then when I'm away for awhile I turn it up to around 70 F so that the window AC keeps the room cool enough to not get too hot when I return and then when I return home I turn the window AC thermostat down to 60 F again.
Window AC units do need maintenance just like Central AC units need maintenance to keep them working properly and cooling properly and to extend the life of the window AC.
You need to maintain the window AC unit by cleaning the filter regularly at least once a month or sooner if it gets dirty sooner.
You also need to at least once a season remove the cover off the back of the window AC and wash the AC out and wash the coils with some soap and water with a brush to clean the AC coils so they can have free flow of the air that needs to pass through them.
A window AC unit can last for 5 years to 10 years and in some cases longer if you maintain it properly.
The average lifespan of a window AC is 10 years although some have lasted as long as 15 to 20 years.
The usage of the window AC also affects how long the window AC will last as well.
The more you use your window AC the less time it will last and the less you use the window AC the longer it will typically last.
If you get 5 years to 10 years out of a Window AC that sees a lot of use to keep you and your home cool then you're doing good.
Keep the window AC filter clean and wash out the Window AC with some soap and water once per year or every few years depending on how dirty it is.
My window AC I take it out of the Window at the end of summer and then take the back off of it and clean any dust and dirt out of it and use a hose and some soap and water and a brush to clean the coils and other dirt and debris out of it before storing it for the winter.
Doing this keeps the dust down and helps extend the life of the AC and also helps the Window AC cool better.
If the coils on the AC are clogged with dust or dirt then it won't be able to suck the heat out of the room properly and disperse the heat to the outside.
So you will notice that the Window AC has to work harder to cool the room down or it may not cool at all if it's really clogged.
With proper cleaning and maintenance of the Window AC you should get a lot of use out of it.
If your Window AC is 10 years old or older you should be prepared to replace it in case it goes out.