I hope someone has experienced this same problem. In my case I don't think it is the dimming issue many have seen.
After sitting dormant for the winter months, I reconnected the battery and went for a drive in my '99. After a while I noticed that the entire Climate Control panel was blank. Nothing works. None of the buttons or rotary controls produce any reaction. After a few minutes with the ignition on, the indicator lamp in the Front De-fog button comes on, and stays on. Cycling the button does nothing. Even turning off the ignition will not turn off the indicator. The only thing that will is disconnecting the battery, which if I don't (or if I don't have charger connected) will run down the battery.
Using the DIC to look at the codes, I noticed that one error code says something to the effect of "HVAC -- No Com". If the HVAC control has lost comunication with the BCM (or whatever), why would this turn on the Front De-fog button indicator?
This is a low milage car (40,000) that spends winters in a warm garage, not a prime candidate for grounding/corrosion issues. That is where I will first look problems (after checking all fuses). I was just hoping the symptoms might be unique enough to point to something specific.

Thanks,
Steve

 

I assume by your description that this is manual a/c. Are you saying you have checked the fuses?

 

No, this is a Climate Control or automatic unit. I have checked the fuses in both fuse boxes that I thought might be associated with the HVAC unit.

Steve

 

I have the same issue hvac is dead and fuses check good. 03 vette dual zone. I am pulling unit to check circuit board. Dave

 

We're starting to see a lot more of this issue lately here on the forum. Have to wonder if there are solder joints giving out.

 

Well, I've pulled the head unit out and will touch up all the solder joints today. You can't always tell by looking at the solder joints whether they are good or bad, but I must say, after looking over both boards, the joints look pretty good to me. I'll still re-flow most of them and let you all know what happens.

Steve

 

I've pulled the head unit out and reflowed most of the solder joints on both boards. Made no difference, still does not work. I really didn't think it would, my unit does not function at all, it's not just a loss of the display. I've checked every single fuse in both fuse boxes and every one is good.

I've inspected the underhood grounds and they seem to be OK. I've also pulled the codes and for the HVAC Module and I get no numeric codes, instead I get a message saying "No Comm.". I assume this means the HVAC control is not communicating with the BCM? I think I read somewhere that the Key Fob Receiver uses the same serial bus/port, and it works fine, if thats of any help.

Anyone got any ideas of what to do next?

Steve

 

Hi Steve, I feel your pain. I'm experiencing the same thing with my 2000 Coupe. My display went dim, then completely dark, then the whole unit stopped working. I have been messing with it all winter. I tried to re-solder the joints as shown in the other thread with no luck.

Once the nicer weather showed up here I decided to put all back together because I wanted to drive it. To my surprise it worked... for about 4 days and then it went out again. I've check and cleaned up all of the grounds under the hood and at the bottom of the A-pillar. I've checked the wires in the door jams, checked the BCM for water damage. I don't know what else to do.

I've scoured these forums with no luck. It seems that the only advice is to look at the electrical thread. The only post I've seen where someone has had somewhat similar issues with the HVAC (and more) was fixed by either cleaning up or replacing the ignition switch.

I would like to know if there is a way to test the HVAC unit to see if it is the problem or the problem lies somewhere else. (Sorry for being so long winded)

 

I'm going to make a pure guess here that the serial buss interconnect is the same one for the BCM, right next to the BCM. Bill Curlee has an excellent picture of this "Star Connector" and as I remember, I think its just a bridge type device, connecting several wires together. It should be hanging to the immediate upper left of the BCM, probably taped up but truly I'm not sure. Anyway, if you can find it, look for corrosion on it and the bridge connection on properly.

 

You can benchtest the HVAC to see if it's "basically" functioning correctly. You'll need a 12v power supply and several test leads. Apply Ground to pin 1 and 12 volts to 5, 12 and 16. Everything should light up and you should see the exterior temp read 69 degrees. Then you can go through the various mode buttons and Driver's temp dial to make sure they operate...

I can take some pics of the test wiring if you'd like... LMK

 

Thanks for the instructions. I will give it a shot this evening. If I run into trouble I may take you up on your offer for the pictures.

Thanks, I checked the Star Connectors and they both looked OK.

If the HVAC Controller bench tests OK I figure I might as well go the extra step and take a look at the ignition switch. Out of all of the posts I've read on this board, that is the only thing I haven't checked out. I will be sure to post my results. (Sorry Steve if I seemed to hijack your thread.)

 

No problem Crooze, sounds like we are both getting some good advice. I'll check the "star" connector first and if that looks ok I'll pull the head unit and test it. Thanks dgrant3830 and tstar. I was just about to plop down the cash to buy a new head unit just to see if it was where the problem is, now at least I can do a rudamentary test.

Thanks again guys, might be a day or two before I can get this done.

Steve

 

Hi there. Not trying to hijack the thread here, but I'm having similar issues too. So I was wondering if I'n in the same boat. I have the automatic climate control, and there is nothing doing on the main display screen in the mornings on my way to work. All the lights light up when I turn my headlights on, but pressing the buttons does nothing. A few weeks ago it would come on after about the first 10 minutes of driving. However on my drive home in the afternoon every day it works perfectly. I had the unit rebuilt about 4 years ago, and it worked great. Again, sorry to hijack, but I'm curious as to some of your ideas. Thanks in advance.

 

Is everyone getting a "U" or no Comms code for the HVAC also? Like Dave stated this isn't the typical "Dim Display" and seems to be more and more prevelant as of late...

Let me check my Core stock and if I have a good one I'd like to do a swap so I can test out one of these totally "dead" HVACs with one of you and check this out...

Tim

 

I've got no codes. Just the No Comms when it gets to the HVAC. I'd be more than willing to swap to let you test it.

 

OK I'll see if I have an HVAC for the 00s...

Tim

 

Tstar, if you are sure about your bench test connections, then my control head must be bad. The only response I get is the backlight lamps around the driver side control **** light up, but the passenger side bulbs do not. I suspect the bulbs may be burned up on pass side. I get no intellegent response from the LED display. Interestingly, after a couple of minutes powered up, the indicator in the Front Fog button lights up and a single segment of the LED display dimly lights up. Just the same as when it is in the car. Sure looks like the control head is bad. Wonder what the cheapest source for a new one would be?

Steve

 

Steve... Can you remove the boards from the case? I believe you need a 1/8" nutdriver to remove the four outer screws that holds the case together and then the four inner screws that holds the power board unto the rear portion of the case...

Once you do that and reconnect the harness between the Display board and the Power board, you can reconnect your test leads and power it up again. Then push on the "241" resistors on the power board, your display should come back to life. Those need reflowed....

Once you can see what the HVAC is actually doing we may be able to determine what's going on with it... I can run down several things that happen, for instance;

Push the AC button, it's orange LED indicator should come on for about 2 seconds then flash 5 times and go out.

Defroster's indicator LEDs should both light up when they are pushed.

You should be able to see all the different air flow Modes show on the display when you push the Mode button several times.

The Driver's Temp dial should change the desired Set Temp as you turn the ****.

You should see the Fan Speed changing on the Display when pushing the fan speed rocker switch.

The Auto button should, well make it go into Auto!

Tim

 

tstar,
I've taken the unit apart again and done every physical thing I can to try and re-make a broken circuit, pushed, wiggled, and sometimes pulled on all components. Even tried flexing the board a little. No difference. Is there any test point on the board where I could check for correct supply voltage? I doubt that a pinout of either IC would be available on the internet, they're probably proprietary GM/Delco part #'s.

I was going to attach an image, but apparently I'm not allowed to.

Steve

 

I know that this thread is four years old - any definitive results for the dead HVAC panel on C5s? Mine's a 1997, not dual-zone. Thanks.