Currently the search work only with an OR operator for separate keywords. However the 3.2 version is almost deployed to codecanyon, which contains this feature. I'm attaching a pre-release version here for you, so you can try this feature now.
Steps for upgrade
0. Make a backup copy of the current search folder just in case. It's located in wp-content/plugins/ajax-search-pro/
1. Deactivate, delete the old version through the plugin editor
2. Install the one I attached here
3. Open up the search setting and save them to refresh the database values and to re-create the stylesheets
On the General option->Behaviour tab you should see now a new option dropdown called “Keyword Logic” where you can choose from 'OR' and 'AND'.Best,
If you like my products, don't forget to rate them on codecanyon :)