Chevrolet Repair: blower air from vents, vacuum leaks, vacuum lines

Question
QUESTION: 1994 S10 Blazer Tahoo, 4.3, automatic, 4x4, 4 door,
While driving and reaching cruising speed, all is fine.  Then if you accelerate, the blower air quits from the face vents and changes to the defrost vents,(on heat, vent or ac)then when you ease of accelerator the air returns to face vents.  Does same if using cruise cont. I have replaced all vac. hoses.
Thanks for your help.
Bud

ANSWER: HI BUD,,UNDER THE DASH THERE ARE WHAT IS CALLED DASH POTS, [ VACUUM HOLDERS]MORE THEN LIKELY ONE OF THESE DASH POTS ARE LEAKING VACUUM[NOT HOLDING THE BLEND DOOR CLOSED ]SO WHEN YOU ACCELERATE ALL THE VACUUM IS DEPLETED WHICH ALLOWS THE DOOR TO OPEN ALLOWING HEAT FROM THE HEATER CORE TO ENTER THE CABIN..IF YOU ARE HANDY YOU WILL NEED TO GET UNDER THE DASH AND CK FOR A VACUUM LEAK..YOU ALSO MAY WANT TO CK FOR ANY VACUUM LEAKS OUTSIDE THE CABIN AREA BY THE FIREWALL AREA FOR ANY BROKEN VACUUM LINES GOING INTO THE DASH. YOU SAY YOU HAVE REPLACED VACUUM LINES,, WHAT VACUUM LINES AND WHERE ???? LET ME KNOW HOW YOU MAKE OUT,,,TOM..

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QUESTION: I changed all the Vac. hoses under the hood, from the distribution valve behind the engine at the firewall to all points they lead to, from transmission to accuator for front differential, cruise cont. etc. I also have tried a seperate vac. reservoir between the distribution valve to the plastic hose going into the cabin, to help hold more vac. to the plentum and inside heat and air controls. It did no good.  The dash pots you mention, are they the same as the door accuators?
Thanks Bud

Answer
HI BUD, DASH POTS ARE THE SAME AS DOOR ACTUATORS PROVIDING THEY ARE CONTROLLED BY VACUUM AND NOT ELECTRIC..IT SOUNDS LIKE YOU HAVE A GOOD SOURCE OF VACUUM GOING INTO THE DASH WORKS..MORE THEN LIKELY YOU WILL NEED TO START REMOVING THINGS UNDER THE DASH TO FIND THE CULPRIT OR GET AT IT..ARE YOU FLEXIBLE ??? I WISH I COULD HELP YOU MORE BUT THIS IS SOMETHING YOU NEED TO JUST START REMOVING THINGS TO GET AT WHAT YOU ARE AFTER..ALSO MAKE SURE THE CONTROL HEAD PANEL IS WORKING CORRECT..MOVE THE LEVERS AND WATCH THE BLEND DOORS TO SEE IF THEY START TO MOVE AND ALSO CK TO SEE IF WHEN MOVING THESE LEVERS THAT THE VACUUM SWITCHES AROUND..HOPE THIS HELPS YOU AND GOOD LUCK,,,,TOM..