Climate control won't change vents
Advanced
Joined: Aug 2002
Posts: 71
Likes: 7
From: Cincinnati Ohio
no sorry, I've got no input from anyone here on where to go now. I'd like to know how much vacuum I should be receiving under the dash at the purple line junction. that would give me a start but maybe that number is not known.
Original Founding Member!
Joined: Jul 1999
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From: Granby, MA
Cruise-In 1, 3, 9. 10 & 11 Veteran
Last edited by XtremeVette; Jun 9, 2016 at 10:18 AM.
5th Gear
Joined: Dec 2012
Posts: 5
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AC control isse
I recently had my intake manifold off to replace the oil pressure sensor and since then I have had an issue with air going to all vents. On the actual AC control unit it shows it changes airflow but nothing actually changes. Any suggestions?
Tech Contributor
Joined: Dec 1999
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
BC
5th Gear
Joined: Dec 2012
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Thanks for the help!
Tech Contributor
Joined: Dec 1999
Posts: 32,910
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
When I owned my new 98 Coupe mine fell off and I spent the better part of an afternoon with a screw driver, flashlight and a mirror and finally got it back on.. SO,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, ,,,, Its possible. 
If it were ME now, I would remove the manifold, lengthen the vacuum line and reinstall..
BC
If it were ME now, I would remove the manifold, lengthen the vacuum line and reinstall..
BC
Advanced
Joined: Apr 2016
Posts: 57
Likes: 15
Bypassing the Vaccum tank?
Excuse my ignorance, but I seem to have solved my problem, wouldn't mind some advice tho
ive identified I have a loss of vacuum at the vacuum tank behind the passenger front fender, I bypassed it and ran the vacuum (from the intake) right into the cabin, voila I have control of the heating ducts! I don't feel any other vacuum lines coming off the tank (isn't there suppose to be something for the air pump?) so I'm wondering if I can just remove the vacuum tank and
Run with the vacuum running straight into the cabin, What's that tank do anyways?
ive identified I have a loss of vacuum at the vacuum tank behind the passenger front fender, I bypassed it and ran the vacuum (from the intake) right into the cabin, voila I have control of the heating ducts! I don't feel any other vacuum lines coming off the tank (isn't there suppose to be something for the air pump?) so I'm wondering if I can just remove the vacuum tank and
Run with the vacuum running straight into the cabin, What's that tank do anyways?
4th Gear
Joined: Sep 2016
Posts: 4
Likes: 0
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Tech Contributor
Joined: Dec 1999
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
If the air comes out of multiple levels or the wrong level, you most likely have a vacuum issue, vacuum controller issue or a damper issue.
I would start with the vacuum source and vacuum lines.
BC
4th Gear
Joined: Sep 2016
Posts: 4
Likes: 0
air direction
In most any car that has selectable level and zone controls, its VACUUM controlled. Vacuum is applied and vented to a vacuum motor (piston/cylinder) and moves the damper to select that level.
If the air comes out of multiple levels or the wrong level, you most likely have a vacuum issue, vacuum controller issue or a damper issue.
I would start with the vacuum source and vacuum lines.
BC
If the air comes out of multiple levels or the wrong level, you most likely have a vacuum issue, vacuum controller issue or a damper issue.
I would start with the vacuum source and vacuum lines.
BC
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
theres a black box that has 2 vac lines 1 goes to inside car thats connected to a purple wire and the other line goes to engine and cruse control i have 3 actuator 1 for ac 1 for heat they both work fine when u switch from any sorce the door that heat comes out of cloes now it on defrost and the air is coming out of front vents
BC
Heel & Toe
Joined: Apr 2015
Posts: 24
Likes: 1
From: apple valley CA
I know this is an old thread but I'm hoping someone will chime in. I followed the instructions from everyone on fixing the vacuum problem for the hvac. Excellent pictures, they helped a lot. I had a broken check valve and the line was missing / broken at the firewall. I now have vacuum all the way to the purple vacuum line. The purple vacuum line will not hold vacuum and when I hook it up, I can hear it leaking in the dash. Is there a common problem for this symptom? I was getting ready to start tearing the dash apart to see what I could find but I thought I would see if anyone else knows anything of this problem... thanks.
Too many hoses to guess.
7th Gear
Joined: Jan 2019
Posts: 7
Likes: 0
Just love the Forum as a resource for Corvette fixes. I have the same issue with low air from all vents on my 2000 C5. Here's what I know so far. I have accessed the vacuum tank behind the right fender by partially removing the fender. I have confirmed that no acid issues exist. A few years ago, I changed my oil sender unit via removing the IM. At that time, I placed an extension line to the small vacuum port from behind the IM. Today, I have also confirmed via my Mighty Vac, I have 6 psi at the vacuum tank. So that's a good thing. I placed an adapter to temporarily connect the good vacuum line to the line going up to the firewall, which in turn gave the controller 6psi, I guess. I thought that this would produce favorable results at the vents, but I got no change. Air is still blowing out of the defroster, eye level and lower vents. This obviously did not fix my issue. I would greatly appreciate any input now. Since I am 66 years old, most of my bending, twisting and keeling days are behind me, but I refuse to give up. Does anyone feel that I need to remove the a/c controller? I did remove it once when I repaired the low illumination issue by successfully re-soldering the factory welds. That was at least 4 years ago and I would think that if I have somehow mis-aligned something, it would have shown up sooner. This vent air issue is less than 3 months old.
Racer
Joined: Jul 2010
Posts: 391
Likes: 67
From: Oak Point Texas formerly okc
St. Jude Donor '16
It should be showing a vacuum. IMHO it is something to do with the line running from the back of the manifold. The indicators of the problem just says that is what it is.
Advanced
Joined: Mar 2017
Posts: 56
Likes: 10
From: Saint Louis Missouri
Recently acquired a 99 C5 with 103,000 miles. HVAC responded to temp but not to mode. I found no vacuum from the black line entering the passenger compartment. The HVAC held a vacuum just fine. I took a different approach for now. Bought a small 12vdc vacuum pump. Wired it into a key on circuit. It pulls approx 13 inches of vacuum. Sufficient to operate the modes. It beat digging thru 22 year old wiring to trace the factory vacuum line or removing the fender. With the HVAC vacuum lines in the passenger footwell along with the fuse panel, it was an easy install. And my modes work as they should.
Racer
Joined: Jan 2000
Posts: 422
Likes: 3
From: Palatine IL
Seems like I have a fault in the vacuum tank. My car is supercharged. Is there any harm if I run a line direct from the manifold to the vacuum block and it sees boost occasionally? Is it worth putting a check valve inline?
Pro
Joined: Apr 2004
Posts: 719
Likes: 21
From: Miami Fl
Great thread and very informative. On my 04 it will randomly stop blowing from the front vents as if it lost vacuum for about 5 -10 minutes randomly. I checked the main vacuum line into the cabin and their is good vacuum all the time. I also checked the vacuum canister and line and they hold vacuum even after the car is off. Without any codes can I assume the head module is bad or the vacuum actuator?? I'm about to make a T and manually route the vacuum to the blend door for the front vents and the cabin recirculation actuator to rule out its a vacuum issue or actuator malfunction.
So far the only thing I've done on the module is upgrade the lighting to LED and resolder the little resistors than cause the display to dim.. anyone know if any soldering issues cause blend door malfunctions?
So far the only thing I've done on the module is upgrade the lighting to LED and resolder the little resistors than cause the display to dim.. anyone know if any soldering issues cause blend door malfunctions?
Pro
Joined: Apr 2004
Posts: 719
Likes: 21
From: Miami Fl
It uses a vacuum canister and check valves to prevent the loss of vacuum while the intake is " boosted" or at WOT.