What is the determining factor for 'and' vs 'or' searches

I have a question on how searches are executed. If you look at my attached example, you can see that I search for "1000 hp". In the first search table, the search appears to be an 'and' search (1000 and hp). However, in the next two tables an 'or' search was performed. Why? Is there a way I can control the how searches are performed?
Thanks,
Dave Wheelock

Thanks,
Dave Wheelock