Ambient Air Sensor Junction location?

I need to know where the ambient air temp sensor comes into the harness with the A/C. It's shown somewhere between the amplifier and the connector at the compressor if I am not mistaken. My temp display is not working and as a result, the A/C won't stay on. A/C has been looked at by an indy shop and a dealer. 100% it's an electrical issue and everything works fine with the A/C as long as you repeatedly press the A/C button.

The harness was messed up by a truck shop in louisiana who put a brake controller in for me. Can't take it back because I moved out of state the next day. They screwed me, and kept the truck till closing time because they know they screwed it up. anyway. Dealer wants a grand to take out the dash and diagnose it.

The connector I am looking for is labeled A37 junction connector (I think) in this photo. I think if I can find that, I can trace it down hopefully repair the issue.

 

All sensors run to the AC amplifier. It is the “ecu” that controls the AC.

Did your dealer hook the truck to Techstream to see if it had any trouble codes in the AC ecu?

What exactly is your AC doing to fail?

Where did the shop install the brake controller? This them mention tapping into the factory harness?

Ambient air temp sensor is right behind the front grill. It puts the outside air temp up on the display next to the clock.

A37 junction is under drivers side dash. Could be near where your new brake controller is.

 

Did your dealer hook the truck to Techstream to see if it had any trouble codes in the AC ecu? --->No idea, they wanted to yank the dash.

What exactly is your AC doing to fail? ---->Comes on, blows cold for a few seconds and then starts blinking

Where did the shop install the brake controller? This them mention tapping into the factory harness?----->next to the hood pop, and yes you can see where they put and removed taps.

Ambient air temp sensor is right behind the front grill. It puts the outside air temp up on the display next to the clock. -----> I know, the display is blank, only shows F

A37 junction is under drivers side dash. Could be near where your new brake controller is.----> It's on the lower left by the hood pop.


With a little update, I ordered up the connector and the 3 wires for it, that go to the A/C Compressor. I used it to learn how to de-pin the factory connector. first I tried Depinning the red wire, dropping in a replacement and going directly to battery +. No luck. The schematic looks to me like the blue one carries + too, so I skipped it. I Put the red wire back and De-pinned the Green wire. Dropped in the replacement and went to battery (-). I have cold A/C, but the button will no longer cycle it off. If the blower is on, It's blowing cold. I live in florida, I have not tried the heater as it is 90 freaking degrees. I'd like to fix it properly and get the use of the button back as well as the outside temp.

It's been broken since march 2019. I had a company truck and this one just sat, only drove it on weekends, if at all, and usually only to the beach. Switched companies, been driving mine every day since. This past monday was the last straw. The clowns I work for had me drive from jacksonville to Bradenton to work 4 hours, turn around and come back. On a good day, that's a 4 hour ride one way. Monday, all the tourists decided to bail and it took nearly 6 hours. Normal Traffic from Tampa to the Turnpike, then it was stop n go for 50 miles as all those goofballs jammed every exit looking for gas, and it was HOT in that cab.

 

By jumping wires directly to your compressor you are bypassing the control panel and ac ecu. You are forcing the AC to stay on 24/7 no matter what.

The system is designed to where the ac ecu reads in data from all the sensors. If they look good it sends the signal to the compressor to turn on and make cold air.

By jumping the red or blue or green ground wire you are telling the compressor to come on no matter what the ac ecu or control panel is saying. This is locking the clutch in on the compressor without the ac control panel or ecu telling it to do so

You need to isolate why the ac is not working properly. The Toyota Techstream software will tell you the trouble codes inside the ac ecu. If the light is flashing it has a trouble code. Somthing is wrong with the data that is being fed into the ac ecu so it’s turning the compressor off after a few seconds.

What I am saying is the wiring between the ac ecu and compressor is fine. You need to be looking at the wiring between the sensor and the ac ecu

 

Boss, the dealer did not want to do that, they wanted to take out the dash and troubleshoot that way. No thanks. Your whole post isn't really helpful. Mine was to ask where this junction is because I think that's where they screwed it up. They tapped into some wires in the driver's side kick panel area before they gave up on that and just ran new ones. I know what sensor isn't working. It's the ambient air sensor. The display is blank. You want to help me find that junction? Scan tool is useless for that.


CLIFF NOTES:
The ambient air temperature sensor info is NOT getting where it needs to go.

Wires were tapped into and then the taps were removed.

I need to find that junction and then the specific wire that carries the signal from the AAT sensor to that junction and then on to the the display and amplifier. This is somewhere in the driver's kick panel area.

unfortunately there are elleventy-fifty wires and multiple connectors.

Can you help with that?

Also, it WILL NOT work if you jump the red to positive, because it is missing ground because that is what the sensor triggers. All I did was repin the connector to keep it grounded.

 

In the drawing, It shows the junction being the first one out of the loom by the firewall. There is nothing connected to it? I don't see another connector anywhere that will reach it or even one that is disconnected.

 

I am probably the best resource on this forum when it comes to Tundra electrical so yes I can help with that. Unless you want to take it somewhere and start shelling out money to get it fixed

More times than not when people just start jumping wires around without really knowing the function/design of the system, they make the problem worse. Also we live in the digital age. That truck has over 10 computers running all the systems each one with the ability to give you trouble codes to quickly isolate what it is or is not seeing. The Toyota Techstream software is the most valuable tool for this by far.


Anyway if you look in my second post I very clearly point out where the A37 junction is under the driver side dash.

The ambient air temp sensor is a basic two wire thermistor. A temperature resistor.

According to the diagram in your first post (which I put on this site) The purple wire is the signal into the AC ecu from the temp sensors. The red wire is ground from the sensor to the A37 junction connector.

At the A37 junction the red ground from temp sensor is tied to the yellow ground trigger from the AC ecu and the green ground trigger to the AC compressor


First thing I would do is make sure you actually have a temp sensor is the harness is plugged into it. It is on the front grill.

After that get the volt meter out and start doing some continuity testing. This will tell you if the wire is a complete circuit on both ends or if it’s broken somewhere in the middle.

I would test from the A37 junction green wire to the green wire at the compressor.

From the Red ground wire at A37 to the sensor in the grill.

From the purple signal wire at the sensor to the ac ecu.

If you really think you have a broken or cut wire somewhere this will tell you

 

Being a junction connector it doesn’t necessarily have to have somthing plugged into it. Can you see the wire colors on the other side? Do any of the look cut or broken.

Can you post a picture of the general area and wires that the other shop messed with. If I can see them I can prob let tell you what they go to or where they came from

 

Junction connectors often have only a mating plug connected into them - no wires. The mating plug has jumpered pins built into it instead of male pins with wires. All of the wires in the junction leave out of the same plug (A37 in this case).
Toyota plug part numbers that junction two connectors together with wires coming out of each connector will be numbered with two letters (like AJ3)

 

You can also see on the blue wire on the left bottom that they poked a probe in that wire, or something anyway

 

Checked that white connector. Red, Green, and yellow are the wire colors

 

Yes exactly what is supposed to be there in pins 5,6,7. I assume none of them look cut broken or spliced?

Next step is test with a multimeter from that junction connector to the other end of each wire. That’s the only way to know if one of them has a break without tearing the entire harness apart.

It is also possible the wiring for the ambient air temp sensor is fine but the shop messed up the communication line that sends the temp signal from the ac amplifier to the display. This would mean the ecu sees the signal fine it just can’t send it out to the display. Once again the Techstream software I mentioned would verify this. It will tell you exactly why the AC ecu is not happy.

I assume the ambient air temp sensor worked fine before it was taken to the shop? Is the ambient air temp the only thing in the truck not working correctly? If the communication line is shorted or broken, most likely a lot of weird things would be going on also.

What year is the truck?