Vacuum and heater AC
 

I just replaced the carb on my 1978 with 351M. The new carb has one less vacuum port than the old one. The missing port was for a vacuum line going into the firewall that I assume is for the heater/AC control head. With car running I found that the line was pulling a vacuum. Now I'm thinking that the control head is bad which is way I have always had warm air coming through when I switch to the vent position. For now I have just plugged that vacuum line. Any thoughts on what I should do with the vacuum line and how to know if the heater/AC control is bad. I will not try to get the AC working unless I fix the warm air coming through issue. Thanks for any input.