How to Recover Deleted Facebook Chat History
When chatting with your Facebook friends, the chat window displays the history for the current conversation. You can scroll up and down that window to read what has been written. At the top of the window is a "Clear Window" link. Clicking that link deletes the chat history, as does closing the chat window or going offline. You can recover your deleted chat history by visiting your Facebook Messages feature, which keeps a chronologically integrated record of all messages, chats and texts.
Log in to your Facebook account.
Click the "Messages" link on the left side of the screen under your profile avatar thumbnail.
Scroll down the list of threads until you come to the one you are looking for. Click the thread to view the latest post in the thread.
Scroll up the page in the selected thread to read its contents. Your chat history is integrated with your message and text history.