1999 Suburban 5.7 with rear AC. Just bought it and noticed I don't have heat.Under the hood It appears to have 4 heater hoses coming out of the firewall. Two of them have been plugged off. The other two run into the engine. One of the plugged lines has a broken plastic valve which I assume is a heater control valve. Went to Advance and they have a valve but it's only a two in two out valve. Where do the other hoses go? Thanks!!