I have 2002 passat wagon GLS 4 motion. I have some issues and not sure where to turn.

1) check engine light has been on for awhile. I took it in to get checked and was told it was a coolant issue (low coolant). my coolant is full now and the light is still on.

2) the little tiny plastic piece that holds the light bulb for my headlight is melted. The dealer says I have to replace the entire wiring harness, but I do not believe that. Is there somewhere to just but the little piece of plastic?

3) my air conditioning has an attitude. It blows cold for 20-30 minutes, then goes warm and stays warm for about the same before switching back.. VW said it was some sensor that was replaced (under warranty) but it still does the same thing. When its cold, it is VERY cold.. but when its warm, it gets really hot and humid in my car and fogs my windows.

Any help would be great!!! thanks..