Heater A/C Control help please!
 

I’ll tell you exactly what I know, so maybe somebody who has worked through this can help quickly or at least point me in the right direction.

The Heat-A/C always comes out the panel. It wont come out the floor and turn the panel off. I investigated the issue so far, and have found that it appears the actuator under the dash is working (I don’t have tools to test it, but I appears to be ok). The door does not appear to be stuck (I can move the door by moving the actuator). There are several colored vacuum hoses under the dash. It appears that the yellow hose does not have vacuum. The blue, red, and orange all work. I’m not sure about the brown.

I have the automatic heater control system, so there is a bank of solenoids behind the ash tray. I can hear some of them working, but I think some are not (those that control the yellow vacuum line, as I get no vacuum on this line).

By using a tech II, I can move the dials on the heater controls, and the Tech II shows that the solenoids are being requested to move. It also appears to confirm that they have moved (I’m not so sure about this). I have also put the tech II in troubleshoot mode, and was able to tell each individual solenoid to move. The tech II reports that they have moved. (again, I’m not sure they are moving, some do, some don’t appear to).

The bank of solenoids does indeed have a vacuum source.

According to the service manual, the problem is nailed down to either the bank of solenoids, or the control unit. I cant seem to figure out which one, or how to tell for sure. The head unit is easy to replace, but $266.00. The solenoid bank is only $60.00, but I don’t see an easy way to get it out. The manual says I have to remove the entire dash, but maybe I can get lucky and pull it out through the ash tray area. It looks very difficult. If I can get it out, I don’t think I can get it back in.

In your folks experience, which part typically fails? Solenoids or head unit?

Has anyone on here been able to remove the solenoid bank through the ash tray area? How did you do it?

Does anyone know how to confirm which part is bad in layman’s terms?
Thanks for any help you can provide.

RE: Heater A/C Control help please!
 

Since nobody seemed to know anything, I took a stab at the solution myself:

First I purchased both parts new. Plugged in the new head unit, it didn’t change my A/C issue.
Plugged in the new solenoid unit and jerry-rigged it to the manifold. Wholla! Working A/C vents.

Knowing I had to remove the solenoids, I used a mirror to locate the mounting screws behind the solenoid bank. By removing the radio, I was able to jam a flexible nut driver behind where the radio mounts, and fish it down to the location of the screws. With a little effort, I was able to get both screws out and remove and re-install the solenoid bank.
If you have to do this job, take special note that the solenoid bank case has a “lid”, which snaps shut holding the solenoids inside the mounting case. Unfortunately this case opens the wrong way, but knowing how it opens you may be able to pop the case open, and remove the solenoids without removing the mounting screws. If I had to do this again, I would try to pop the lid off the case, and just remove the electronics. It would make the job incredibly easy.

RE: Heater A/C Control help please!
 

Thanks for the connotation that no one here knows anything! Helps greatly!! Good luck in the future!

If you had searched, you would have found the vacuum logic which would give you insight into what component was at fault. As the auto climate control is quite robust, you were probably the first active person here to have to replace the solenoid.

I am glad that you were able to fix it yourself. Seems that most people would rather berate others than take the initiative themselves.

RE: Heater A/C Control help please!
 

I didn't mean to imply no one knew anything period, the statement was in regards to this specific repair. Not everyone can know every repair issue.

Also, I have the GM service manual for the vacuum logic, although the manual is very poor from what I have used it for so far. Vacuum logic would not provide insight as to which component was at fault. It will only lead you to the solenoids, which it did.
If I knew how to use a multimeter, and had better electronics knowledge, I may have been able to determine it was the solenoids. Or if I knew how the Tech II reports data and component operation. (there is no vacuum between the AC control unit and the solenoids If you have a manual unit, the head unit has vacuum on it). Either way, having solved this one, and proved the solenoids could be removed without removing the dash as is stated in the service manual, I wanted to help others who will surely have this problem.