I have an 83 Trans Am and my ventilation system doesn't work for ****. Today I was poking around under the hood and I noticed this black box mounted on the firewall, right under the cowl on the driver side. On the left side, there are two ports for what appear to be vacuum lines. One line is missing altogether and the other is cut after about two feet. Just out of curiousity I blew air into the line and it made this whistling sound, the identical sound my car makes when I turn on any setting for the heat or air. Also it just blows air out the defrost. Does this black box have anything to do with the heater etc? Where are these lines supposed to connect to? I would really like to get this straightened out cuz its hot in the summer and real cold in the winter here. Thanks in advance.

 

It's a vacuum "accumulator". One of the lines is supposed to go to manifold vacuum, and the other one goes toward the A/C control head. The air flow is directed by doors that are moved around by vacuum diaphragms.

Your HVAC will do exactly as you describe if it has no vacuum.

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"So many Mustangs, so little time..."
ICON Motorsports

 

OK so how do I hook it up to manifold vacuum? Would it have anything to do with the little pipe plug thats screwed in behind the carb? What do I need to look for on the AC control head? Which hose goes where? Thanks for being patient, this car is a mess under the hood and I just want everything to work right.

 

since it is just a vaccuum box, I think it would akmost be safe to remove it and cap the two connections that the hoses from the box went too, though I am no expert on the function of that box.