Okay, I've heard of this problem before. I know it has been adressed, but i haven't found it in the archives.

What is happening-A/C, vent...everything comes out defroster vents. The question is...Where are the gates and vaccum servos? What is the easiest way to get to them? Any tips and tricks? --Thanks all--

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Mint black/black 1987 T/A GTA 305 5-speed, 55K,
3.45 factory POSI,Taylor wires, hurst comp plus shifter, K&N conical rig, AFPR, coated shorty headers, no cat, no smog, 3in. mandrel-bent single exhaust, flowmaster, TB air foil, 160 stat, SFC's, lower control arm adapters, Aluminum Driveshaft, ported upper and lower, Mobile ES and 10 disc, kickers all around and q-logic kick panels...Perf 350, rear batt, lowering springs,cowl hood, & NOS coming soon!

 

Don't worry about about whats behind the dash, the problem is probably under the hood. The doors in the dash need vacuum to operate, wich comes from the intake manifold. You need to trace the vacuum line from the engine to the firewall, and make sure its intact. Also check to make sure the vacuum reserve canister isn't broken. It will also have a vacuum line to it.

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If you live in Southeastern US, check us out!
South East Thirdgen

GM Master Tech
ASE Master Tech + L1
Savannah, GA

'87 Trans Am
S/D TPI retrofit including functional PassKey,
22# injectors,
Whatever chip I feel like burning,
JET AFPR, Ported Plenum,
TB Coolant Bypass, Custom Cold Air,
SSM SFC, KYB Shocks, Boxed LCAs, Wonder Bar,
8mm Accel wires,
Flowmaster Exhaust,
16" GTA rims,
Corvette Servo,
3.73 Posi
4wheel Disc Brakes

'97 Bonneville SSE

 

is that the black plastic ball tucked in the fender?
i have this same problem, and I know that ball is broken, but I can get the right vents to work sometimes
thanks

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90 IROC 5.7l (L98)
ram air, K&N's, air foil,Flows

LIKE A ROC

 

hrm, i'm interested, since mine only blows...half a$$ed. Although the blower motor itself sounds like it's blowing good enough to make it winter inside the car when it's summer outside. Always did wander what that black ball was though...anyone care to elaborate? maybe some diagrams of the vacuum lines?

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89 IROC-Z 350 TPI

-Flowmaster Catback
-Performance Resource Chip
-700R4 (Rebuilt) Too much done to actually list
-K&N Airfilters
-Ported Plenum
-2.77 Gears (not much to brag about but eh, its there)
-MSD 8.5 mm plug wires
-Gutted cat
-!AIR
-Gutted Air Boxes

 

Ideally, engine vacuum is 20" of Hg at idle. At WOT, that vacuum goes to 0". At 0" of Hg, all your vacuum accessories will cease to operate (i.e. HVAC doors in the dash). The vacuum reserve "ball" is to maintain vacuum on the sytem even if the engine is not producing any. There is also a checkvalve to prevent the vacuum from bleeding off into the intake, much like the brake booster.

------------------
If you live in Southeastern US, check us out!
South East Thirdgen

GM Master Tech
ASE Master Tech + L1
Savannah, GA

'87 Trans Am
S/D TPI retrofit including functional PassKey,
22# injectors,
Whatever chip I feel like burning,
JET AFPR, Ported Plenum,
TB Coolant Bypass, Custom Cold Air,
SSM SFC, KYB Shocks, Boxed LCAs, Wonder Bar,
8mm Accel wires,
Flowmaster Exhaust,
16" GTA rims,
Corvette Servo,
3.73 Posi
4wheel Disc Brakes

'97 Bonneville SSE

[This message has been edited by GMTech (edited May 16, 2001).]

 

to address the original question, there are a few things that can be causing it... first of all, do you hear any vacuum leaks at all while the system is in use, no matter which vents the air is coming out of? what usually ends up being the culprit is the rubbery mating surface of the vacuum harness on the vacuum selector switch. there is a trick i've heard on this board to swab a little vaseline inside of each of those tubes, or to replace the harness (lots of work), or to modify the harness, which is what i did. so, let's start by seeing if you have a vacuum leak that you can hear...

KAM

 

Yep, sure enough a vaccum leak. I think it's coming from behind the radio. ...I meant to mention that in the original post. I've already checked the vaccum lines going into the plenum...they are fine. I've been through that engine compartment many times, and I haven't seen the black plastic ball. Where is mine on an 87 gta? I've seen it in my buddy's camaro..but never on mine. Hmm. Must be due to the leak behind the dash which is why i was asking originally where the vaccum servos were located and how to get to them. Thanks

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Mint black/black 1987 T/A GTA 305 5-speed, 55K,
3.45 factory POSI,SLP cam, SLP runners, Taylor wires, hurst comp plus shifter, K&N conical rig, AFPR, coated shorty headers, no cat, no smog, 3in. mandrel-bent single exhaust, flowmaster, TB air foil, 160 stat, SFC's, lower control arm adapters, Aluminum Driveshaft, ported upper and lower, Mobile ES and 10 disc, kickers all around and q-logic kick panels...Perf 350, rear batt, lowering springs,cowl hood, & NOS coming soon!

 

OK - chances are you just have that bad manifold pad thingy I mentioned earlier. The A/C control head has to come out (not completely) so you can get to that vacuum switch. It is held in place by (2) 1/4" screws, and the "pad" of the manifold is attached to it by a couple of those goofy washers - don't know what they're called, but they just pry off. Take that manifold pad off and put your finger over the purple tube, which is the vacuum source. (with the engine running, obviously...) If the vacuum noise can't be heard, then vacuum is good up to that point. Try the easy way first, put you some vaseline in those tubes with a q-tip, and apparently that'll work. What I did to fix mine was to cut that manifold pad apart so that I had all the tubes separated, and then shaved off the excess pad material, then re-attached each tube individually to the back of the switch, fastened on by a little zippy-tie. Works like a champ ever since. You don't want to replace that harness, it's alot of work. Be sure you note which tube goes where if you have to go with the cut method. I hope this helps...

It's a little easier to work on if you take your stereo out, but it's up to you...

KAM

[This message has been edited by thunderstick (edited May 17, 2001).]

 

The vacuum ball is underneath the battery tray.