The first thing you do to help this situation is to completely, unapologetically, 100% take yourself out of the middle-man position. EVERY SINGLE TIME this happens.
If they get angry at each other, they need to learn to work it out and talk rationally and reasonably to ONE ANOTHER. Every time you act as the go-between, you let them off the hook with this childish type of behavior, and you actually perpetuate the cycle. So, stop that part now.
Now, for the next part, which may sound a little harsh, but I can only go by the little bit you have here. Your husband is acting like a child. He won't talk to his son??? He's abdicating his role as a parent, and you're letting him. We get mad at our kids sometimes. All of us. But, we get a grip, and then we deal with it.
I get the need to have a cooling off period sometimes when an argument is really tense or when there is an impasse, but at some point, the parties involved need to calm down, collect themselves, and maturely face the situation. Why does your husband refuse to do this? And what kind of role model is he being to your son with respect to healthy communications?
Can you imagine getting mad at your boss and refusing to talk things over with him/her? That's the stage your husband is setting: I get mad. I retreat. I refuse to talk. I let somebody else work it out for me.
I don't think this is how you want your son to communicate in the important relationships in his life, so start by modeling better for him. Tell your husband you'll no longer act as interpreter or middle-man and insist that he start dealing with his son directly. If he doesn't know how, there are tons of books on the subject, or if it's really that difficult for him, then therapy would be the next option.
Good luck, stay out of it, and let them both learn!