Strange Heater/AC vent operations.


Old 09-11-02, 08:56 AM
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Strange Heater/AC vent operations.

First off, I asked a question on how to get the shifter know off my 1992 Cavalier; I went to the Chevy dealer and there is a sort off ďUĒ nail type pin on the part of the shifter knob which faces the heater assembly.

Now, to the reason I needed to get the shifter knob off.

Normal operation for the heater vent seems to be having problems, ALL heat/AC is coming out of the two vent outlets in the center of the dashboard. No matter what position (Def, B/L, Heat, etc.) I set the lever to ALL air comes out of these two vents with ONLY a slight amount of air coming out of the other (one by each door, two near floor) vents.

I inspected the assembly and it seems to be working fine, meaning that the lever is indeed operating the wheel which adjusts which vent is to flow the air; also, the vacuum hoses seem to be in working order with no holes, but thatís just from observation, I didnít test them.

Why is all the air being funneled to the center vents? Do I have to dissemble the dashboard and check the vents themselves?

Has anyone seen this problem before?


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Old 09-11-02, 09:29 AM
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Usually the vacuum wheel at the back of the A/C controller goes bad and causes this.

Alternatively, check the vacuum lines going to the vacuum reservoir (typically a round plastic ball with a vacuum line going to it) and any and all vacuum lines. Cracks in these will cause the vents to go haywire.

It's one of those two problems.
Old 09-11-02, 09:36 AM
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Thanks Joe_F

You're to fast for me.

After posting I decided to do a search, I know, I know; I've got it A** backwards.

I found a post by you and Cheese:


probably have a vacuum leak, and/or a bad vacuum check valve. Look on the firewall for a vacuum line that runs through to the interior. Follow that line back toward the engine until you find a small plastic disk or cylinder shaped piece attatced to the line. That is the check valve. Vacuum should move through it one way, but not the other. Check that line also for vacuum. If it doesn't have good vacuum, then it's pinched or leaking.


I agree with Cheese, but typically the problem on most GM cars is a bad vacuum wheel (about 8 bucks) at the back of the A/C controller. It goes bad and the air comes out everywhere but where you want it to come out

Thanks again,

Old 09-11-02, 02:02 PM
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Used a "junk yard" vacuum wheel but it didn't work. Just exactly what goes bad on it? Looks like two pieces of plastic to me, what can go bad? Decided to order a "new" one from GM anyway.

Also, decided to try the "vacuum check valve" but GM didn't know what I was talking about, does this go by another name? I told them it was a "vacuum regulator valve" but they should have known what I was talking about, or should I have been more correct with naming what I wanted.

Just exactly what does the check valve look like? What I found was a disk about 2 inchs in diameter and about 1/2 inch thick with three lines coming out of it; is that it?

Old 09-11-02, 06:00 PM
Join Date: Dec 2001
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it does usually have 3 lines coming off of the chek valve but it is very small about 3/4 inch in diameter and a little over an inch long it is usually located near the firewall but can also be along the drivers side fender if you have had the vacum lines off of the control switch start the engine up do you feel any vacum at any of them you should at one, if you dont you need to check under the hood for broken vacum lines, and at the vacum resoirver the reoirver may be in an odd spot if you dont see it under the hood look under the left fender in front of the drivers front wheel.

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