Automatic Climate Control is not working?

2004 BUICK REGAL
175,000 MILES • 3.8L • 6 CYL • 2WD • AUTOMATIC
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ATARAX
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Hey, I have similar problem like in this post:
https://www.2carpros.com/questions/no-ac-control-display#last

I have the car listed above LS and there is nothing on the climate control screen. Sometimes the red warm dual lights only light up (bottom right see attached picture). At night the light of some buttons lights up, but there is nothing on the display. One day, I started the car, the screen came on just for a sec and then nothing. When I tried to set the temperature, it turned off. So far, all the controller does is blow a little of hot air only (randomly). I turned the key to on. I measured voltage and on C5 and I got 3.15V. I checked the 10 fuse (was ok), but I changed anyways. I was trying to trace the brown wire from the cabin fuse box (Second picture). Measured voltage on third picture for C5 and I got the same reading 3.15V. I was trying to locate the S233 splice but did not succeed. I just have basic car wiring knowledge. I also unplugged the relays from the engine fuse box, I tested resistance and apparently, they are okay. Following this procedure: https://electrouniversity.com/how-to-test-a-relay-with-a-multimeter/

Finally, I was reading other posts, and I also have the same issue with the cruise control, (mirrors are working though).

https://www.2carpros.com/questions/buick-regal-2000-regal-cruise-amp-fan-system-stop-working-same-time

The post explains the reason is the ignition switch, but it seems a job for a professional.

Not sure what to do, to be honest.
Aug 21, 2024 at 5:05 PM
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STRAILER
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I don't see the picture? To me it sounds like the HVAC control module is out, but I would check the ground and power inputs and if okay replace the module. Here is a guide to help and the HVAC system wiring diagrams so you can see how the system works and which wires to test for the ground and power inputs. Please check the G200 ground on the right side of the dash.

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

Here is how to change out the HVAC control head in case you need it. Check out the images (below). Please upload pictures or videos in your response of any problems so we can see what to help you with.
Aug 22, 2024 at 9:56 AM
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ATARAX
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Hi Ken,

Thanks for your prompt reply.
Just to keep the thread. I'm going to attached the pictured that I mentioned on my previous post and add more details about the measurements I did.

I measured the orange wire (back of the plug) and I got 12.41V and when I did the brown wire, I got 3.15V.
Aug 25, 2024 at 9:57 AM
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ATARAX
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Keeping going withe thread. I managed to get an used climate control and installed yesterday night. (I haven't checked the G200 because I couldn't locate it. How does it look like?)

I connected the "new" climate control and there is more backlights on when "night driving mode" is on (picture 1) but still the display is off and controls do not respond. There is just a bit of warm air coming out, and sometimes I can hear the blower kicking on for a couple of secs and the it goes off. It happens a couple of times while driving, but not all the time. The cruise control light is still blinking all the time though.

Hope this can give you more input.

Thanks again for your time!
Aug 25, 2024 at 10:10 AM
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STRAILER
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I would use this guide to see if the HVAC control head is getting power and ground, please check the wiring diagram above for the termails.

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

If it is not getting power or ground it will not light up.
Aug 25, 2024 at 6:38 PM
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ATARAX
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Uhmm, Yesterday and today, it lights up and works for a couple of mins randomly. When setting the temp the display goes off but keeps blowing air. It might be the battery?
Aug 29, 2024 at 3:55 PM
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STRAILER
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That is how solid-state electrical acts when it is going bad. There is no battery inside the HVAC control module FYI.
Aug 30, 2024 at 9:43 AM