If a marker is clicked near the top of the map viewport, the infowindow loads outside the viewable area and the map must be dragged to see infowindow content.
Ideally I don't want the map to auto pan. Is there a way to load the infowindow in a different direction, e.g. if the marker is at the top of the viewport to display the infowindow in a downward direction.
There is an example that used to be part of the Google Maps JavaScript API v3 Code Samples, that has moved over to GitHub, named: SmartInfoWindow. It does exactly what you are describing. Check into the underlying code and that should get you going in the right direction.
No, you can't open google's default infowindows in a different direction since you don't implement your own infowindow class. But you can disable auto-pannnig simply passing TRUE to disableAutoPan property of InfoWindowOptions object like documentation said.
来源：https://stackoverflow.com/questions/9881502/google-maps-v3-info-window-opening-outside-map-viewport