Rear AC not working

"AC unit" - what does that mean? What was replaced? If you do not have rear climate controls, are you certain cold air should blow in there from the front controls? I'm not familiar. I can't imagine how you cannot control rear air temperature or flow -- I'll refer you to seek guidance at a shop near you. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops