Have you tried skype? Maybe if he could see his Dad, he would at least have some interaction.

It may be that because he doesn't understand and can't express himself, that he is trying to protect himself. If he doesnt talk to his Dad, then it wont hurt, ITMS?

I wonder if you could get him to draw or make something for his Dad - that may help him express himself. He probably doesnt know why himself. I know a lot of males dont know why they do the things they do or dont do, even as adults. It's harder for them to understand their own emotions.