1999 Hyundai senata V6 150,000

I am having a problem with the air conditioning and heating system. They do not work at all. It doesn't even sound like it kicks on. I don't not even get fresh air when I open the vent. I checked the fuses and had them tested they are all fine I also checke dthe belts and they seem fine as well. I am stumped as to what it could be and how much it might cost.