engifineer

Now, I dont think it is quite time to celebrate, take long romantic showers together, etc, but I know I found one potential issue that may be the cause for the 2007 HVAC problem. For those that do not know the issue, some earlier 07's had an issue where the HVAC lights would stop working correctly. Some or all of the lights will work normally. When you turn on the headlights, most of the HVAC lighting will turn off.

I have one in my hands right now that had that exact issue. Granted, they had done an LED swap on it at some point, so it is possible that this problem was caused inadvertently then, but being the exact symptoms of the more common issue, this could be the culprit.

The fix it to re-solder T302. This is a transistor (it has 3 legs) that is located just below the hazard button on the front of the board. The on I was sent to test on had 2 of the three legs loose on this. And it appears that the original solder joint from the factory was faulty (a cold joint). Being that it is bad joint, tapping it the right way will sometimes make it all light back up. This would explain why some can bang on the HVAC console and make the leds come back on, or why the issue can easilly pop up after taking the board apart for an LED swap.

Using a test harness, I was able to test the fix and it worked for this one. I have some other items to fix for this person on the LED swap itself, but I should be sending this back out to him tomorrow so he can put it back in the car later this week. I will update again when I find out for sure how it worked in the car. Since I dont have a 2007 tC to test it in, I will wait till he plugs it back in the car to say for sure.

However, whether or not this is THE cause of the issue, it is one possible item that will cause the same problem. I will take a pic of the device in question once I verify the fix and let others know. If anyone else has this issue and wants to check this in the meantime, feel free to contact me at engifineer@gmail.com with questions or post on here. It basically takes touching a soldering iron tip with a tad of solder to the pins to fix the solder joint.

O5_TRD_tC

nice easy fix!

engifineer

Hopefully this proves to be the cause on all of them like this. If so, it will be simple to check for and repair when working on the 07's.

O5_TRD_tC

it may be the issue, because while removing a defective 07 hvac, it worked one last time for me. And then it went out on me again.

riboflavin

iTrader: (2)

good, I might try this on my old 07 hvac

trrocks03

*hoping*

theunclesam

Think this could cause a problem with the dimmer circuit seeing around 3v or so even when the parking lights are off?

My problem is described here: https://www.scionlife.com/forums/viewtopic.php?t=187522

Socalheatz

i didnt know there was a problem w/ the 07 hvac. but now that i think bout it.. they do turn off when i turn off headlights, they're not suppose to do that??

engifineer

The buttons and LCD should all be lit up when the headlights are on. If they go out when you turn on the headlights, you have one with the issue. This occured a lot with the 07's, at least earlier on in the year model. The dealer typically just replaces it, but for those who have already done the led swap or have dealers who wont co-operate, they are stuck with a broken HVAC.

engifineer

I am not sure if this could relate to the issue in the thread that was linked above. I would have to trace further on the vehicle in question to be sure.

I also mapped out most of the lighting control circuitry on the 07 HVAC last night (on paper for now) to go along with the led maps I created back in 05... so if I work on many more issues, I will have a schematic of the entire board

Socalheatz

ah, unfortunately i have an 07, might have to try this fix sometime

engifineer

Reading your previous post again, it is normal for the lights to turn off when you turn the headlights OFF. The issue is that on some, the HVAC lighting turns off when the lights are turned ON.

mystik

iTrader: (1)

hmm, i might have to get that HVAC out again lol...didnt think i would need to but its becoming annoying sometimes seeing the lights on, other times off...

Garage1217

iTrader: (5)

Very good info Thanks Dave! I can put the theory to test locally as I have a failed 07 unit that I can get my hands on later this week that has the standard "beat it with a hammer to get it to light up problem"

ippskidder

watching.

theunclesam

I'm going to take my HVAC out and see try your solution. Couldn't hurt anything. I'll update you if it fixes the problem.

engifineer

Great, let us know! If that is the issue, you will probably be able to see the bad connections with a magnifying glass. His was actually only fully attached by one leg, so when I touched it with a meter while figuring the circuit out the whole thing moved which tipped it off for me.

BZinn1

What no romantic showers Dave.......and we all had our hopes up....... ...great find on those HVAC panels.....should sell the answer to Toyota so they can save soem money and get us all a new tC out sooner.

engifineer

bumping to see if anyone tried it yet...

theunclesam

I might give it a shot on Sunday. I'll let you know.