My A/C is going crazy. The top vent on the windshileds blows hot air, the dash vent blows no or little air, unless I increase the fan (auto mode, keeps the fan in the middle) then cold air comes out, also hot air is coming out thru the floor vent. The dash computer reads - (minus) 40 deg. F. I have a 1998 528I with 118k miles. How much is this going to hurt my pocket or is this a simple fix? I live in Ft. Lauderdale and temps are already in the 90's.