1978 vacuum port new carburetor

[sjckn]

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.

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[74 Harley]

You can use a T fitting to restore vacuum to the heater controls. If they are not functioning correctly you need to get under the dash and start checking the various hoses that connect the vacuum canisters. If they are all good and things still aren't working get a little hand vacuum pump and check each canister. With the car running you may also be able to hear where the vacuum leak is.