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riceburner98, thanks for the fix, my light went out today. This problem sounds simular to the Subaru Forester clock issue, bad solder, but their issue affects every car produced for a good number of years. Goto the Forester forum and look up clock fix, there are 15+ pages of thank you's
Bart
 

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I just bought my wife a 2007 tC a couple weeks ago that's exhibiting exactly these symptoms (HVAC panel light turns off when headlights are turned on, flickers occasionally). I'm pretty handy, but have zero soldering experience. Still, I only got a powertrain warranty with the car, so I guess I'll go shopping for a soldering iron this weekend and look for panel removal directions.

Edit to add: It looks like there's some handy soldering directions from the same author as this post, and also some directions for panel removal. Nice one stop shopping, thanks!
 

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I can verify that it worked for me. I bought the car with the known issue. I checked out this forum if there was a solution, (my final deciding factor :p ) followed the DIY fix, and BOOM, done! :)
 

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Discussion Starter · #44 ·
Glad it has helped more people! Stupid little issue, but at least it is relatively easy to fix with some soldering practice :)
 

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fixed!

I realize this is an old thread, however, we just bought an 07 scion tc and experienced the problem of having no HVAC lighting when the headlights are on. Found this thread, followed the instructions, and experienced an easy solution. Big thanks to Engifineeer and all the others who gave a great DIY tutorial.
 

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Background of Issue
Many of the early 2007 tC's have had issues with the HVAC lighting working intermittently or stopping all together. If your HVAC lighting only works sometimes, goes out when the headlights are turned on, etc, this is probably your issue. If the car is under warranty and the dealer is going to fix it, they simply replaced the HVAC unit. However, those that are out of warranty or have done an LED swap probably arent always so lucky. The remaining alternatives have been either buying a new HVAC (around $500) or purchasing a salvaged one ($50 - $100).

The Fix
I was finally able to get one of these sent to me that I could plug into a test harness and test. I spent some time mapping out more of the lighting control circuit (I had mapped a good amount of it previously during design of the LED mod for the HVAC, but not the input and dimmer control portion) and found the issue. I have since had one other person try this fix on theirs successfully as well, so while this may not be the only possible cause, chances are this is the one causing the common issue. The issue is a couple of cold solder joints on the legs of one device. The fix is detailed below.

1) Remove the HVAC. There are plenty of threads and DIY writeups on the forums detailing this part, so I wont add all of that here.

2) Remove the HVAC from the housing so you have the bare board.

3) Locate T302 on the front of the board right under the hazard button. This is a 3 legged device (a transistor) that controls part of the lighting function.

4) With a low power soldering iron with the tip tinned just a tad, reheat the solder joints on each of the three legs so the solder reflows.

5) While you are at it, go ahead and check T303 right next to it.

6) Plug it in and test. The lighting should now act as normal!

A pic is provided below for reference. If you have any questions on this or have the issue and this fix does not work for it, feel free to contact me on the forums regarding it. Going forward, I will check every 07 HVAC that I perform led mods on for this and resolder the device for good measure to prevent the issue from popping up.

[/QUOTE]
I have a similar problem, the a/c, up and down button are not working. Everything else work. Does anyone have any advice?
 

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Discussion Starter · #51 ·
Hey folks. Have not logged in here in a very long time! I have a ton of messages about the LED swaps and related items, but just letting folks know if they see this that while I still have the tC I have spent most of my car related time developing and tracking the s2000 and have not had much time between that, co-driving an ND for autox and life in general so have missed most of these messages. My apologies to those that were waiting on answers!
 
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