Another thought:
Even if you call and don't get much response from him, you've opened the door. My eldest brother had a son when he was 18, and (long story) lost touch with him. The boy's mother contacted my brother when the son was about 12 years old, and they met. No other contact for several years, but they reunited when the son was in his twenties, and better able to understand the circumstances, and they see each other quite frequently, now.