I would check the fuse that serves the A/C (IHKA) Control Panel, F60 if built BEFORE 3/1/2007, and F61 if >3/2007. If you had disconnected any connectors in the dash area when replacing the head unit, then check those as well. Here is the TIS Circuit Diagram for later 2007 models, and also the Installation Location for the two connectors, X01217 & X01199:2007 328i Sedan. Battery died during a new head unit install. Charged battery for about a half hour. Now air will only blow out of defrost and will not cool. Read online about a possible transport mode from low voltage? Anyone else had this issue?