No Mid-Level HVAC Output - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 08-13-2011, 11:29 AM   #1
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Default No Mid-Level HVAC Output

1996 Bonneville SE 120k miles

The vacuum servo that sends air out the mid-level (dash) vents is no longer opening.

It started by being "lazy," but now it doesn't open at all, making for a HOT summer here in Dallas.

A/C is working fine-you just cannot send it out of the vents (only the defroster or heater vents).

Shop says entire dash must be removed and wants $600 for labor plus parts.

I have the Pontiac manuals (all 30 pounds of them) and it doesn't say that.

Any hints how to get at the servos (presumably on the left side of the heater box) the "EASY" way?

Car has every option, is almost like new (even the paint and leather) and still doing 24mpg around town and 30 on the highway, and is TOO nice to get rid of! I drive other cars all the time, and STILL think the Bonne is a damn decent ride!

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Bob
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Old 08-15-2011, 08:14 AM   #2
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The easy fix is to pop the hood and pull the engine cover (if it'* there) then follow the brake booster line from the booster to the rear of the upper manifold. Right before it goes into the manifold, there is a nipple and small hose that should be connected. That small hose feeds the vaccum that holds the diverter to the middle vent position.

Check that out first. Those diverters don't fail often, but vacuum lines come unhooked all the time.
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Old 08-15-2011, 10:39 AM   #3
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Quote:
Originally Posted by BillBoost37 View Post
The easy fix is to pop the hood and pull the engine cover (if it'* there) then follow the brake booster line from the booster to the rear of the upper manifold. Right before it goes into the manifold, there is a nipple and small hose that should be connected. That small hose feeds the vaccum that holds the diverter to the middle vent position.

Check that out first. Those diverters don't fail often, but vacuum lines come unhooked all the time.
I didn't check that only because the other servos work fine, moving the air to the defroster vents, or the heater outlets.

It' possible there is a slight leak causing the least strong servo to not work.

Are you saying the hose you mention ONLY holds the diverter in the middle vent position?

Bob
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Old 08-16-2011, 09:33 AM   #4
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I didn't check that only because the other servos work fine, moving the air to the defroster vents, or the heater outlets.
Bill is right. Check the rubber ends on the plastic 1/8 inch lines. They age and rot with heat. A leak lowers the vacuum available. There also are connections on that plastic line at the T in front of the accumulator (take off the relay center cover to see the bundle of electric wires and the plastic vacuum line) and are connections at the storage tank under the right front fender in front of the wheel. That tank may be cracked.

Then you're inside the car where the black line goes through the firewall on the right side. Take off the plastic hush panel under the dash. The violet vacuum line connects to the black line from the engine side. They pull apart. Check your vacuum there if you want. Check for vacuum there with the motor running.

Also before pulling that apart, run the motor to build vacuum. Turn it off and leave key at ON so the blower motor works. Then push different buttons on the dash control and listen for the sounds of the diaphragms moving. If you hear the diaphragms for about 20 seconds of push and they slowly weaken, you've probably got a good vacuum storage tank and connectors at the T and inside.

Most likely you've got the nipples inside the plastic connector on the corner of the programmer box sucking shut. The AC blue line does it first as theplastic softens with age and heat.

This is an early article about cutting the plastic connector out of the lines. The programmer box comes out and the top snaps off and your have access easily to put in short lines to connect the inside and outside colors--make a list first: the colors inside the programmer are different than the outside line to the diaphragms.

http://www.imcool.com/articles/airco...acuum_line.php
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Old 08-18-2011, 02:19 AM   #5
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Great info-
I'll get on it.

Thanks-
Bob
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