Climate Control System (HVAC) Can't be controlled

[kapinossa]

Automatic climate control system can not controlled during summer and winter operations. Problem unresolved for over one year. The display flashes during initial startup as per design to indicate a system problem (stored fault codes). Specific codes do not point to any sensor. Will post specific codes (two) tonight, but essentially point to effect not a possilbe cause. System operates during summer and winter in essentially full cold and full heat depending on startup sequence. Outside air temp reading correctly. Engine warmup that delays heat working fine. Heating airflow adjusts from defrost mode to cabin heating postions just fine automatically when commanded by the programmer after riding in car for several minutes. However, any manual mode commands are not working. First indication of problems developed occurred when commanded temp adjustment required several degrees (greater than 4) to effect a system change. Then finally the system started not responding to any temp change requests. Problem appears to be in programmer but all doors and sensors seem to respond when commanded by the programmer. However, the programmer does not respond to operator requests. Any suggestions to possible manual override operator actions or rewiring. Or is there a potential vacuum leak that could result in uncommanded operation? The programmer runs around $750. Would like to control override heater door position somehow or work the system manually. Any help would be appreciated.

[Honest Jim]

Kap,
Sounds like the same problem I had recently. Here in Northern Ohio last month My 94 Bonneville out of the blue just started blowing cold air. I read all I could, checked wires vacuums, etc. to no avail. I noticed that if I ran the thermo setting down to 60 and let the a/c kick in, then run it back up to about 75 it would work, for awhile. Also, that if I popped trannie in neutral and shut the engine off and restart, it would be fine for awhile. (Though, I don't know if that is any good on either the engine or trans) but in sub-zero temps you do what you have too. I finally broke down and took it to a mechanic.
He was able to wire the "door" or flap open for heat to enter the cabin, and all settings work fine. Though I believe the flap actuator?? which is in the dash needs replaced. He said it is a job for you have to tear the dash apart to get to it, and would run about 400-500 $. I did not delve further into it with him at the time, as it was late night and it took him all day to track down the problem. I will look for my receipt in order to give you an idea what he did do if you like. But, he did say he had to reprogram something, I don't recall what it was. I was happy to just have constant heat. Hope this helps you. Jim

[kapinossa]

Jim, Thanks for taking the time to provide your insight. Your situation sounds very similiar. I have previously run the temp all the way down to 60 and the system started to respond also. Since I have had this problem during both seasons, getting the system to respond has been a challenge with allot of trial and error. Currently, being in Maryland with several weeks of sub frezzing temp the demand for defrost has been critical to continue operation of this vehicle. I have found the following to work most of the time in the winter weather:
1. Prior to turning the car off, shutdown the system with the OFF button, wait approx 5-10 seconds and then turn off the engine.
2. To begin operating the vehicle, immediately after engine startup, I hit the AUTO button with the TEMP setting of 78 def F (setting that I left on all of time).
3. The defroster starts to blow air once the water temp climbs above 100 deg on the guage.
4. If cold air blows out instead of hot, I wait approx 10 seconds with cold air blowing in and system still in AUTO, I pull off the road and shut the engine off.
5. I wait approx 5-10 seconds to restart car, system was left in AUTO prior to shutdown in this case. After restarting the engine, the system (almost every time) starts pumping out heat to the defroster. The system display then starts flashing that it has a code stored but this does not change any of the ducts and heating continues.
6. I leave the system in AUTO and accept its programing of the ducts, which seems OK in general (a slow transistion to the floor vents). If I get too hot, I will select the OFF position but always runs the system for 30 seconds prior to going to step 1 at the end of the trip.

During the summer, the operation is different. I never select AUTO until the system display stops flashing. The system runs in full cold and I always keep the temp set at 74 deg F. I usually shut the system off prior to shutdown. In addition, if no cooling I will usually try to run the temp up to the max setting and back to get the A/C to cut in. I have been very successful in running the system for cooling but need to double check my exact steps that I used this past season. The procedure worked 100% of the time for cooling but heating has been the harder nut to crack.
Bottom line, going thru these steps to allow heating and cooling of the car is a pain in the butt. I was hoping to find a process or wiring change to over-ride this totally automatic system. I am very interested if you have any additional details on the mod that you had done. I own the GM Bonneville service manuals but haven't been able to isolate the heater door which is commanded even when the system is in the OFF position. I previously owned a 93 Bonneville with a manual HVAC system which worked fine but I really like the auto features of my 96 HVAC system (untill this issue has popped up). Steve

[jkinney]

Hey guys, I recently encountered the same problem, and looked into it a little bit. I stopped dead in my tracks when I heard (from quite a few) that unfortunately, this is a dealer item only. They have to "Re-calibrate" the climate control with a "Scan2" tool. Now, I own both a OBD-l, and a OBD-ll scanner, and this is not what they are referring to. I have read where there is a nylon gear that can drop a tooth, or get stripped that will mess with the door, and as far as the memory issues on recalling last temp, and turn on, turn off issues, blowing cold air, I'm told re-calibrating is required. You guys are putting some good effort into it, and would love to hear if you find another way of eliminating taking it to the dealer. Good luck.

[kapinossa]

jkinney, on my last trip to the dealer to read the HVAC codes the tech used a scanner that I have not seen before. I wish I could id the tool but assumed it was the tool referenced in the service manual. This tool provided the codes and was able to drive several of the controls independently and observe the commanded positions of the system. No specific troubleshooting was performed but the tech noted some very strange behavior. I have not tried to observe a potential gear tooth missing but will attack this item when the weather provides a break. I have not heard about recalibration or any mention in the service manual but there are allot of things that I can't understand or explain on my HVAC system performance and response. I really appreciate you taking the time to provide your insight and will provide an update on my progress. Thanks again, Steve

[sysfx]

I had the same trouble as you discribed. Erratic heating and A/C and the display flashing on startup. I replaced the Air Mix Actuator whith a new one from the dealer ( 92 $ CDN) and everything works now. I take it apart and it was a broken nylon gear (due to cold wheather) that made the HVAC controler to log errors. It was a full day of work to replace because you have to take out the complete dash and floor console to have access (do not forget to disable the airbags before working around them). It is under the right airbag in the back of the compartment. If you take out the glove compartment you can see the actuator rod and the air mix door throught a hole in the airbag frame. The rod can be uncliped from the door and you can move the door manualy whith a long screwdriver for temporary usage. You can see a pic of the broken gear in the actuator im my gallery.

[kapinossa]

Sysfx, Thanks for you thoughts and the great photo of the air mix actuator. Your notes on the scope of the effort to replace are super. I will attempt to view the actuator and hope to determine if this is the root cause. I failed to mention that the door movement does make a dragging sound and I originally thought this could be caused by excess fiction due to misalignment. Maybe it is due to a boken component in the air mix actuator. I have never been conviced that the HVAC programmer is defective but the erractic behavior has had me confused. Thanks again and I will provide update once I am able to get behind the glove compartment.

[CincyRick]

Guys,
Just wanted to say thanks to all for saving me about 700USD. My dealer identified my problem as the programmer and said it would be over $900 to replace (580 for the part!!!!) So I said thanks, no, and headed to the web where I found your posts describing my problem exactly. I did some experimenting and could re-create it as you all did. In about a week my actuator completely stuck open and we were having great weather here (not NOW though.) So I found a radiator / heater specialist and left the car with him. I told him I thought it may be the actuator. He pulled and replaced it for less than $175 ($54 for the part.) I'm SO happy to not only have my excellent automatic heating/cooling system working but to have saved enough for a weekend away. Thanks for taking the time to post.

[Jed Rule]

Had the same problem on my son's Bonneville. The shop manual says "Step 1, remove the dash panel". Here's how I did it - down and dirty: remove the glove box and observe the programmer actuator thru the hole in the air bag support bracket. You should not be able to move it by hand (or a coat hanger). Using a hole saw, cut two holes about 4 inches apart in the front side of the bracket for the air bag just behind the glove box. Connect the holes with a sawzall to allow a 2 by 4 inch access hole. Be careful not to go too deep or damage the air bag case. Disconnect the temp control rod and wire plug from the actuator. Remove the front screw for the programmer actuator and break it loose from the back screw. Remove the back screw and take off the broken tab from the old actuator. Install the back screw but leave it just a little higher than it was before. Notch the back tab on the new actuator to allow it to be slid under the back screw. Install front screw and tighten. Install wire plug. Start engine and set temp to 90. Wait 1 minute for arm to adjust then push rod to full heat and snap back on to actuator rod. Reinstall glove box. Total time: one hour.
The engineers who designed this should be shot.

[kapinossa]

Jed, Thanks for the approach of not removing the dash. I am still dealing with this issue. I am past the point of work arounds. Your solution sounds allot better than the manual. I will need to review the area to make better sense of your procedures. Hope to attack this weekend if the storm leaves MD alone. Thanks again.

[UNCLECC]

Jed????,

Reading your post on the easy way to replace the actuator you mentioned that you SHOULD NOT be able to move it by hand...

Well, I can move mine by hand, had to move it from hot air to A/C..

Does this mean there is something else wrong?

One day my A/C just started blowing hot air..worked fine the day before..read your post, looked into it and was able to move the door by hand..
Bad vacuum? or what else could I look at?

Thanks in advance...
And yes...the engineers should be shot, well, maybe tar and feathered...

[hamyers]

Originally Posted by Jed Rule

Had the same problem on my son's Bonneville. The shop manual says "Step 1, remove the dash panel". Here's how I did it - down and dirty: remove the glove box and observe the programmer actuator thru the hole in the air bag support bracket. You should not be able to move it by hand (or a coat hanger). Using a hole saw, cut two holes about 4 inches apart in the front side of the bracket for the air bag just behind the glove box. Connect the holes with a sawzall to allow a 2 by 4 inch access hole. Be careful not to go too deep or damage the air bag case. Disconnect the temp control rod and wire plug from the actuator. Remove the front screw for the programmer actuator and break it loose from the back screw. Remove the back screw and take off the broken tab from the old actuator. Install the back screw but leave it just a little higher than it was before. Notch the back tab on the new actuator to allow it to be slid under the back screw. Install front screw and tighten. Install wire plug. Start engine and set temp to 90. Wait 1 minute for arm to adjust then push rod to full heat and snap back on to actuator rod. Reinstall glove box. Total time: one hour.
The engineers who designed this should be shot.

Hi Jed, Well, I like your approach but at this point don't see a way to follow it. (I will try to attach a pix. I'm new to the forum.) The bracket in my '95 bonneville is about 2" high so I can't see cutting a 2 x 4 inch hole. The bracket looks like it might come out altogether. I will be out of town for a few days and will try that upon my return unless someone knows of a reason not to.
Thanks for your time in sharing this with us.
Howard