Embraers do silly things with temperatures from time to time. It counts as NSB - normal system behaviour and generally get fixed with software, assuming nothing mechanical has failed. But until a new release is issued, you have to deal with what you have. Unfortunately, the ECS synoptic page will give you little to work with. What would I have done? I would have assumed Pack 2 has failed (because the problem was in the rear) and followed the checklist. That would have resulted in a descent to FL310. Had that not worked, tried Pack 1. I would have left the bleeds alone because all they do is supply the air; and you had enough of that. The next step would have been to annoy the bypass valves by altering the temperature. 12 o'clock is a good position to start with. Sometimes all they need is a nudge to get them working.
What is essential is that snags like this get written up and reported immediately because you can't fly an aircraft without temperature control.
PM