Sorry, just short for Heating Ventilation and Air Conditioning system. I get nothing but the hot air you would expect when it's dialed to the hottest setting, even when I have it on max a/c and set at the coldest setting. Same with all other combinations and settings. Air's always hotter'n hell. I get no codes, there's no info stored in the computer about, no noticeable vaccuum problems. I was hoping you had similar symptoms so that I could be optimistic about getting off cheap for once