Actually the book calls it an HVAC programmer. I remember someone posting about his or her vents not working correctly and though I'd share my progress with the same situation. It's a 96 and stuck in the defrost vent position.

Let me start off by saying if you need to access the programmer part of things get ready for a real sore back. It's located under the driver’s side to the right of the column against the firewall. It comes out but with great difficulty. You'll also twist your body into positions you didn't think possible.

The first thing I noticed on mine was a "remanufactured for Delco" sticker on it leading me to believe someone had tried a repair in the past. This box has four or five electro-mechanical solenoids inside to divert vacuum to the correct vacuum actuator. As I was taking this programmer out the vacuum line bulkhead from the car just fell right off. I thought "great I'll just push this back on and everything should work. Wrong, first the thing wouldn't push back on for the life of me and getting your hand in there to perform the task isn't easy. I did manage to push it back on and everything seemed to work for like five minutes. Vent positions changed and everything.

After a while it reverted back to defrost and there it sticks. In the manual there are supposed to be DTC's to aid in troubleshooting. However nothing really related to vent positions. But there does seem to be some initialization processes to go through.


I did tear the box apart and look for something that may be causing a vacuum leak on the manifold connecting the solenoids, found nothing that would look like a problem so it boils down to something telling that box to divert to defrost for some reason. Even though you've selected something else like ac vents.

So as soon as my back is up to the task again I'm going to dig into the switching part of this box with a meter and see what’s happening. If indeed the defrost solenoid is being activated or the selected vent solenoid is activated.

Something is going on to make this thing get all confused. I checked the vacuum source and it's fine.

I'll post any further progress.

 

My '96 does the same thing, only blows our of the defrost and on the floor. This past summer it would do that and then switch to the correct vents after 15 or 20 minutes. I've been told it has to do with not having enough vacuum to move the doors (or not having any vacuum at all going to the programmer). Isn't there a relatively common problem with the connector that's used where the vacuum lines go into the programmer? Let me know what you can find out... my back is bad enough, I don't want to go under there without some good info...

Vinnie

 

It's more than just the vacuum bulkhead or weak vacuum. That may be the case for some, I eliminated that problem as a cause. When I'm done figuring this out I'll post any tips I come up with.

 

The loose connection sounds like your problem and there are no trouble codes for vacuum faults. By design, GM applies vacuum to the defrost door at all times (Electronic or Manual Controls). Lose the source, gravity takes over (some doors are spring loaded too) and all you get is defrost. To rule out the dash controls, which send low voltage signals to the Programmer for door position, you can check for vacuum at the defrost door actuator. That's usually red or tan or both, your Shop Manual will have a vacuum line schematic. If there's no vacuum on either line, there's a source problem; either in the engine compartment, the connection at the Programmer or with the Programmer itself. If you do find vacuum, then you are going to have to see if the low voltage signals are being sent from the dash. I doubt you have that problem since it worked temporarily with a good vacuum connection.

 

Well tonight I got it working! I'd like to say there was some intricate diagnosis involved and pat myself on the back. However it seems as though it WAS that bulkhead vacuum connector after all. One thing I did do though was cut down those little **** on the HVAC programmer bulkhead a bit. Anytime I tried to push the connector from the car onto it, it just slid right back off after a while. Cutting down those **** and smearing a bit of silicone dielectric grease on them made the part from the car slide on real easy and much further. It's much more secure. I believe it's a **** poor design!

I'm wondering if there IS supposed to be a retaining nut on that bolt that sticks through. It would be unbelievably difficult to get one started and tightened. We'll see how long it stays put without one. There wasn't one there when I took it off.

One thing you can check for is a click sound from under the dash when you select different vent positions. Unplugging the fan motor outside makes it easier to hear them. If you hear those clicks you know everything is operating correctly and you probably have a vacuum leak or no vacuum at all to the programmer.

Pretty much if you can see the display, change vent positions, adjust blower speed and hear the clicks the programmer is working and has B+

Hope all this helps someone; this is truly a pain in the **** to get to so be prepared with some new curse phrases. Write some down ahead of time for reference or just be creative on the fly.

 

I have mine OUT of my car right now.... also a 96. I got a nut from the hardware store, and will use that to tighten down on the vaccume connector. there is also a metel retainer ring on there from the factory, but obviously those do not work so well.

I had to take out my seat to get under there. I'm 6'2". now I'm 6'1" !!
hopefully tomorrow I'll get it back together.

I started a thread about this 2 days ago....

 

I thought about putting a nut on it also. If you do, you might want a washer sized so it just fits between the hoses also. I fear the nut will just slide right through the soft rubber of that connector and make things worse. Food for thought.

 

Does anyone have any pics??

 

I would have taken some pics but my frustration level was so high I didn't need the distraction of stopping for a kodak moment. I apologize for that.

Just take your lower panel off the drivers side and twist your body under there. Look directly above the gas pedal with a flashlight and you should see the vacuum bulkhead attached to the programmer. If it's anything like mine was it'll be hanging on by a thread. It'll have differnt color vacuum lines coming out of it.

 

Yeah, I've taken that panel off and touched the programmer with a finger, don't remember seeing much of the vacuum lines. I didn't take that metal panel off, so I'm really hoping (praying...) that it's easier to get to without that panel there.

 

there is a metal springy retainer buried in the connector. that will act as a washer. hopefully I'll be able to contort myself tonight to get under the dash.............

once again, I recommend taking out the seat.

 

I can't get mine to work properly. put on nut on the stud, and NOHTING. still blows out the defroster vents. I'm thinking mine is shot.
I know the connector is bottomed out.....

any other hints ??

 

Just make sure you have vacuum to it first - that's the black line. If it's not there, you will need to poke around the engine compartment to find out what happened to it. Use the vacuum diagram to locate the source.

 

I ran a new vacuum line from the intake to the passenger compartment because I could not locate the break in the line.

 

yes indeed, I do have vacumme to the conector. it was fairly strong. I put my finger over it, and I could definately feel it.

I may have to replace the "box".
any idea how much they are ??

Is there anything in that box that is fixable ??
I never even opened it up.

 

Usually $200 or more and though anything can probably be fixed with the right knowledge and skills, the innards in that box exceed mine and there are no replacement parts. For OEM, the Last Detail - www.tld-corvette.com - might have the best price. If you have the shop manual, you might also want to go through whatever troubleshooting chart there is to rule out the dash panel. I'd at least see if vacuum is getting to the defrost door solenoid. As I posted earlier, GM universally uses red or tan for that line. Solenoids should be mounted on the left side - looking forward - of the heater box.

 

Apperantly this is another screwed up design by gm.I also have a 96 and it is doing the same thing and allt4 your info is great now i know what i am looking for any more info appreciated....

 

Only thing I can offer here is something I've said before. Make SURE you can hear the vacuum solenoids clicking when you change positions in the programmer. Sick your head under there and listen. Helps to have the car in run but not started. I'f you can hear those clicks the thing is working. You're problem lies elswhere. It still could be a vacuum leak somewhere the programmers vacuum manifold. But as far as electronically the clicks tell you it's functioning.

I had mine open and it's really not that complicated untill you get into the logic. But the vacuum switching couldn't be simpler.

Don't discount cutting those **** down a bit on the programmer. Mine just would not work untill I cut them back a bit. The opening on the **** is very tiny for some stupid reason and I could see them getting clogged very easily.

 

ask and you shall receive:

http://www.batee.com/corvette/acrepa...oard/c68.shtml

 

Just so you know, a 96 is completely different from those pics in that link.