In normal console app I have this
Environment.SpecialFolder.LocalApplicationData is C:\\Users\\Simon\\AppData\\Local\\
In Windows service
<Remember that the services run under a different user profile (can be a LOCAL_SERVICE, NETWORK_SERVICE, etc.) If you'd like them to be the same, run the service under your user profile (You can specify this ServiceProcessInstaller.Account property when you create the installer, or in the Services manager of windows).