Auto Air Conditioning & Heater Repair: A/C blowing through Defrost Vent 78 GMC van, vacuum line, gmc van

Question
Have not had any work done in a while.
Turned my a/c on this week and the cold air is coming through the defrost and bottom vents where the heat is to come out.
On the dash/underside there is a large round ball that has a small air line coming from it but nothing on the other end, plus I found right beside it a T with 2 other air lines hooked with one part open.
I pluged the line in and still the air will not come out the A/C vents only the defrost and bottom.

Answer
Check the vacuum line that runs from the engine compartment and goes thru the firewall and in under the dah to make sure that the line has vacuum in it as when there is NO vacuum to the inside controls on this vacuum line this is what happens.


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