Proper Fridge Temp for Fermenting Sourdough

Hello,

I have recently started working with wild yeast breads, and have encountered several recipes which direct the baker to retard the dough for a number of hours, during which it proofs slowly.  In my case, the dough doesn't seem to proof at all.  Even after several days.  

I think my fridge is too cold, but I turned it down because dough was proofing too fast at the lowest setting.  Now, I'm trying to find the sweet spot, and I'm wondering, what temperature am I shooting for?  I guess I'm looking for a temp that ferments dough in 24hrs, as that is what many recipes call for, or something close.  

Any help is greatly appreciated.  Thanks in advance!!