Defogger problems of the 2002 Mercedes Benz ML500

I have 2002 mercedes ml-500 and my climate control does not works and blowing cooled air all the time even when I selected to full hot. I did buy mercedes shop manual and as I was reading the service bulletins issued by mercedes manufacturer I found that the factory is aware of this issue the a/c system sometimes does not produce heat or cooled air. Mercedes conformed that certain control units part numbers have low voltage problems which causes this and the want the car owner to replace the a/c control unit with the updated part number 163 829 57 89 at the car owner expense because as they say it is not safety issue? well can that be when you don't have heat in the very cold / snow weather as we have here in boston? as far as I am concern this is a safety issue when it comes to heating the windshield in the bad winter states. Please let me know if my complain makes correct.