Arguments are okay as long as there is some point to them. If you want to diffuse the tension so you can both discuss the problems at hand like adults, begin by listening to their side. Try not to raise your voice when you answer, no matter how angry you are. It will just turn into a scream-fest. Don't dredge up unrelated matters. Instead, focus on the present. Try to see the problems through his eyes and lead with answers that begin with "I understand your point but here is how it looks to me..." If you refuse to raise your voice and continue discussing the matter rationally with him, he will calm down soon enough and you will be able to get to the bottom of the issue together without tearing each others' throats out.