Hello,
I recently picked up a higher mileage '07 460 (127k) that started exhibiting some strange AC behavior. I managed to find a simple solution that might help others who have Techstream access (I have the Amazon clone).

Basically, what was going on was the old "AC turns off and then is reset to 75 upon starting" symptom. Once you gave it a few moments and turned on the AC (manual or auto) when changing it to face vent setting, it wouldn't work, or occasionally it would only turn on the passenger side and allow only outside air into the driver's side. Also, I noticed the recirc door wasn't moving and was stuck open.

Of course, having just purchased this car, I figured the previous owner had broken the door for the filter box and discovered some way of disconnecting it and was hiding the fact it was broken. Hahaha the paranoid "oh no did I miss something horrible" feeling of buying a used car.

So I had a look and didn't see anything weird and listened and didn't hear any clicking or anything telling. I thought I'd try hooking up the ol' techstream and watching realtime monitoring.

It didn't give me any obvious codes, but what I noticed is that no matter what i pressed regarding indoor/outdoor, techstream said "Auto", and the vent settings weren't displaying changes either.

So, before I started unscrewing things, I found a little setting under Body Electrical / Air Conditioner / Utility / called "AC Servomotor Initialization" . Maybe you already know about it, but I couldnt find any mention in a quick search. So, I read the screen, clicked Next and ran the test. A few moments later, the recirc door closed, face vents came on and BOOM it all worked again!

I have no idea if this will be a permanent fix, but it worked for another hours worth of driving. Even if I have to occasionally reset it, its way cheaper than a dealer visit and easier to reset it than ripping the dash apart looking for problems.

If you are having issues, I'd bite the bullet, find yourself a Techsream cable and version that works (that last part is kinda tricky), and give this a try. It worked for me and I didn't have to turn one screw. It was awesome.

Hope this helps someone

UPDATE- Problem reoccurred 2 weeks later. Was able to reset it again. Techstream returned error code B1497 which is an AC communication bus failure. This could be something as stupid as a bad contact or wire. I will be poking around in the not too distant future and look for common faults. I repair smd electronics devices by trade, so perhaps I can unlock the mystery of why this is somewhat common.

UPDATE 2 - As a first step, I have unplugged the wiring harnesses to the AC amplifier and cleaned the connections and reseated them securely. When reattaching them, I made sure to not let the cables pull at all, as the original layout had wiring that was pulled very tight. Since I have done this, I have not had the issue reoccur over these last 2 weeks since . But at the same time, the temperature has dipped as we enter fall. So if this is related to heat or stretching allowed due to warmer temperatures, I wont really know until the temperature rises again. I will keep this post updated.

UPDATE 3
Repair is still working! I think it was simply the lack of slack in the harness causing a poor connection 👍

 

I found this setting recently after replacing my heater core and changing a couple of the servo motors. I could not figure out why the new/used motors were still throwing codes until I searched all over the web and found Toyota/Lexus documents about reinitializing the servos and AC amplifier whenever you disconnect the battery or replace these parts.

 

my car has the "AC turns off and then is reset to 75 upon starting symptom. A Lexus specialty shop checked and told me $850 to fix it, but the shop said not worth to fix it since all I need is to manually turn 75 down to whatever temperature I want. I forgot the name of the device to replace...
Not sure if we are talking about the same issue. What is Techstream Access, no idea what it is

 

Hello. Sounds like the shop probably is quoting for a new AC amplifier. They're probably right, but $850 is a whole lot of money if you can still switch the temp with the controls. If youre so inclined, you can acquire used AC amplifiers for $75-100 (new is like $750). Mine would cease to control the AC system, but the buttons would still show that it is doing something. My issue sounds similar, but different symptoms that are a bit more severe.

Techstream is a suite of tools that allows you to test, monitor and edit parameters in your cars various electronics via your computer. You can google it for a boatload of info. Cheap Techstream clone cables go for around $20, a real Toyota approved system starts around $2k and requires a subscription and some credentials for certain access.

 

Did it reoccur by any chance? Or fixing the wiring harness properly seated to the AC amplifier worked.. I have the same issue the AC auto light comes on, then a message appears AC turned Off, then everything works normal, I have scanned for codes and I get b1497. Could it be for some servo not working properly?

 

Hello, yeah the repair has held. No more b1497 for a couple of years now. It was just the tension on the wiring harness pulling the connector from making a solid contact, causing a communication error.

​​​​​​I'd start with checking wiring as it's pretty easy and essentially free. Just gotta lay on your back on the passenger side floor. I can't walk you through it, but if you're remotely handy it's obvious when you look at it.

Dont forget to try the reset procedure in Techstream

 

thanks for sending me the picture

 

@SENSAY813 you probably want to delete your email address from a public forum post if you don't want to be destroyed with spam or worse.

Under the glovebox is a cover. There are 4 tabs along the front you unclip with your finger, no screws. Take that off, and close to the center console there are 3 wiring harness/connectors. Can't miss em.

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unabee - An extremely helpful topic. I like how you went in and edited the original post with followups. Very helpful. I may look into the cheap techstream clone cables you mentioned. What else is needed to along with the cable?

 

@7milesout if you really want to test everything, you need a multimeter and the wiring diagram. It's not entirely necessary because You can just press on the wiring or jiggle it while the AC is running and see if it turns back on or changes settings.

ULtimately it would be best to check for continuity from chassis ground to the ground pins. But if disconnecting it and getting a little slack then plugging it back in fixes it, that's not hyper critical to know what pins specifically are not touching. Results are results.

I wouldn't unplug it while it's running though. I'm not sure that could cause some hiccups.

​​​​​​Techstream is just so useful. You'll use it for sure even if not in this case.

 

I don't have any problems with my AC. I was just noting on how well your first post was updated, very helpful. But I am interested in the TechStream clone stuff.

 

Thanks!
I guess I just feel like it's my responsibility to have an update if I opened the post. I mean, I can't complain about the millions of other frustrating go-nowhere posts if I don't update my own.

There should be a law! UPDATE YOUR POSTS!!