Run app as a different user (automator) i'd like to be able to open an app as a different user.
For example PC1 is my main account and PC7 is my secondary one. 

I can achieve the effect in terminal using

su - pc7 
insert password
/Applications/Application.app/Contents/MacOS/ApplicationName

How can i use the automator to make a script/app whatever that does this by a simple doubleclick?

Thanks
You can not trivially launch graphical applications as another user.

A Proxy Process is Required

To launch a graphical application as another user, that user must be logged in to a graphical session and have a process running within their session able to launch your desired application.

Prior to OS X 10.9, this could be approximated via the launchctl command. See How to launch a GUI application in another user's graphical session? for a detailed discussion.