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This can also happen with 2011 Sienna and Highlander.
If you have this problem you'll notice the AC blows warm air and code B1479 may be set. The A/C blows warm air because the ECU/AC control computer won't engage the magnetic clutch on the A/C compressor because it sees a "faulty signal" from the compressor flow sensor.
Unfortunately this sensor is attached to the compressor (not sold separately) and Lexus's solution is to replace the compressor. The estimated parts+labour cost is around $2000.
I manage to study the problem a bit more and want to share my learning and solution. I found the flow sensor is still works but the voltage range it output had degraded over time. The A/C computer expects 3.8 to 4.2 V from the sensor when the A/C is off and below 3.8 V when the A/C is ON. (the lower the voltage the more refrigerant flows). On my Lexus the flow sensor output was 3.70 V when the AC was off, so the A/C computer panics and won't engage the system. Using Toyota/Lexus' techstream software I manually engaged the compressor and found that the A/C cools just fine. More importantly though, the AC flow sensor was working! (you can see the flow rate fluctuate)
Therefore the problem is that the sensor voltage had dropped below 3.8 V when the A/C button is off. All it needed was a little boost (in my case, from 3.7 V) so that it'll fall within the valid range. In my case, I want to multiply the 3.7 V by 1.07 = 3.96 V. To scale up the voltage I used a non-inverting operational amplifier. You can buy all the component from Amazon/digikey for less than 30 dollars. The output of the AC flow sensor is fed to the amplifier, and the output of the amplifier goes to the AC computer. Inserting this amplifier made the A/C system work again.
If anyone is interested in this solution please let me know. I can post more detail on the repair and the design of the non-inverting op/amp. Basic steps are outlined below
1. Get Techstream cable/software from Amazon/ebay and connect to your car to verify the problem (i.e. flow sensor output below 3.8 V and that the cooling system works when the compressor is manually engaged)
2. Remove the glovebox to gain access to the A/C computer (there are many steps involved, including removing the SRS knee airbag on the passenger side)
3. Design a non-inverting operational amplifier (this is easier than you think, check wikipedia article on operational amplifier)
4. Insert the amplifier between the compressor flow sensor and A/C computer. The amplifier power supply and ground should use the same ones as the flow sensor (pin 30 for power and pin13 for ground on the AC computer). The flow sensor voltage is fed to pin 7. you'll have to cut this line to insert the amplifier.
5. enjoy your A/C go spend $2000 somewhere else!
Mine is a 2013 Camry, shares same AC sensor.
Placing a little piece of neodymium magnet on the sensor (held in place by the snap ring) was all I did to get my AC working again.
The AC sensor definitely has some magnetic properties in it. My understanding of the problem is that the magnetism wears out due to heat, which in turn affects the required voltage.
Easy fix; my AC works ever after Magnet on the sensor. Polarity matters
I looked at Wikipedia and after I cleared the glaze from my eyes from seeing all those diagrams, I think you should start a side business building and selling these non-inverting operational amplifiers. I could install one, but no way would I attempt to design and build such thing. I recall building a guitar amp in high school that did not work until my friend's father, an electrical engineer, tinkered with it.
I used LMV321 from TI as the op-amp. It draws current in the uA so this is no problem for the AC computer. I'm pretty sure the compressor flow sensor draws more
I'll try to see if I can post some pictures. I had to make the circuit mechanically capable of withstanding vibration. trying to make all cables short and all component soldered.
I used LMV321 from TI as the op-amp. It draws current in the uA so this is no problem for the AC computer. I'm pretty sure the compressor flow sensor draws more
I'll try to see if I can post some pictures. I had to make the circuit mechanically capable of withstanding vibration. trying to make all cables short and all component soldered.
Dear y7wu, I have the same problem with my RX 350 2010. On my Lexus the flow sensor output was 3.75 V when the AC was off. Can you pls post me the design of the non-inverting op/amp. At this moment I solved this problem by slide resistor. I cut wires from flow sensor befor A/C Compuner and inserted between them the slide resistor. I used 7, 13, 30 pins on the A/C Comp and have placed by slide resistor 4 V. By this way I engaged the compressor.
Your solution is better because you leave flow sensor to work.
Sorry for my English because I live in Minsk (Belarus) and my first language is Russian.
The circuit is in the diagram below. I used R2=600 Ohms and R1 = 10,000 Ohms.
Vout = (1+600/10000)*Vin=1.06
For you Vout will be 1.06*3.75 =3.975 which is right in the middle of the sensor range.
As I mentioned before I used LMV321 from TI as the op-amp, If you want to use a breadboard then you will need a different op-amp because the LMV321 does not fit on a breadboard.
LMV321 has a datasheet that you can look at. It tells you the pin of the circuit so you can hook it up like the picture shows
I used a PCB from work and chip 600 and 10K ohms chip resistor. You can use a sliding resistor also or bigger resistors.
I recommend testing the circuit before inserting into the car. You can input 1.5 V from a AA battery and use 5V supply (easier way is to get it from the computer USB port, cut the wire and get 5V) and check you get 1.5*1.06 = 1.59
The circuit is in the diagram below. I used R2=600 Ohms and R1 = 10,000 Ohms.
Vout = (1+600/10000)*Vin=1.06
For you Vout will be 1.06*3.75 =3.975 which is right in the middle of the sensor range.
As I mentioned before I used LMV321 from TI as the op-amp, If you want to use a breadboard then you will need a different op-amp because the LMV321 does not fit on a breadboard.
LMV321 has a datasheet that you can look at. It tells you the pin of the circuit so you can hook it up like the picture shows
I used a PCB from work and chip 600 and 10K ohms chip resistor. You can use a sliding resistor also or bigger resistors.
I recommend testing the circuit before inserting into the car. You can input 1.5 V from a AA battery and use 5V supply (easier way is to get it from the computer USB port, cut the wire and get 5V) and check you get 1.5*1.06 = 1.59
Hope this helps
Hi y7wu
Thnak you very much for your detailed reply and recommendation. Its will be usefull for all owners of Lexus cars.
The circuit is in the diagram below. I used R2=600 Ohms and R1 = 10,000 Ohms.
Vout = (1+600/10000)*Vin=1.06
For you Vout will be 1.06*3.75 =3.975 which is right in the middle of the sensor range.
As I mentioned before I used LMV321 from TI as the op-amp, If you want to use a breadboard then you will need a different op-amp because the LMV321 does not fit on a breadboard.
LMV321 has a datasheet that you can look at. It tells you the pin of the circuit so you can hook it up like the picture shows
I used a PCB from work and chip 600 and 10K ohms chip resistor. You can use a sliding resistor also or bigger resistors.
I recommend testing the circuit before inserting into the car. You can input 1.5 V from a AA battery and use 5V supply (easier way is to get it from the computer USB port, cut the wire and get 5V) and check you get 1.5*1.06 = 1.59
Hope this helps
hi there , , can I use arduino ( nano ) for this job .
y7wu, thanks for this post ... I have the same AC issue with my 10RX, got the TechStream sw installed and confirmed DTC code B1479 on my vehicle, with AC off, flow sensor voltage is 3.68v.
By manually engaging the magnetic clutch, AC compressor was running fine and system was cooling just fine. So my next step would be getting some LM321 op amps ...
y7wu, thanks for this , i just became a memeber today thanks for this as well to admins.
Please allow me to start when the problem my ac problem came about.
May 5, i brought my car to dealership, for summer tire re-installation from winter, change engine oil . I also asked them to check for squeeeking noise from the belt when its rainy and wet.
Tire change done, engine oil change done,
For sqeeking noise they told me that my serpentine belt and pulley needs to be replaced, they also told me that im due for transmission oil change , car is at 64,000 miles.
So i agreed for all those to be done, including a break job, replaced 2 front rotors and pads.
I questioned why all those replacement but somehow i agreed and those problems fixed.
Now here is the new problem,, 2 day after i got the car, got warmer here ,,and put on my AC,, there was no cold air coming out,, tried the heater there was heat. I have used the ac and was working fine before i took it in for those repair jobs. Now i dont have AC. Brought the car in today to check for AC problem,, they said its the compressor and ac cluthch giving error code B1479, the same code that is mentioned in this section. It shall cost me with their estimate about $1800 for a jobber replacement part with 1 year warranty. Thats too much money , and im still convinced that the mechanic must have messed up my AC system during all these other repair manipulation. i complaoined and got to nothing, they insist that all the repairs didnt have anything to do with AC. So im reading all these posts here, and question is , was this issue a recall bulletin,,? Im going to read thorugh this quick cheap fix of yours, and perhaps ask someone from my work if he can do this job for me. So i shall be posting furthere as i go along for other questions most likely. Thanks again. I appreciate your thread.
have the same AC issue with my 10RX, got the TechStream sw installed and confirmed DTC code B1479 on my vehicle, with AC off, flow sensor voltage is 3.68v.
By manually engaging the magnetic clutch, AC compressor was running fine and system was cooling just fine. So my next step would be getting some LM321 op amps ...
How long did it take you to open all coverings to get access to the AC amplifier connector?
Hi the following wasnt part of my 1st thread, somehow it got attached. Thanks
"have the same AC issue with my 10RX, got the TechStream sw installed and confirmed DTC code B1479 on my vehicle, with AC off, flow sensor voltage is 3.68v.
By manually engaging the magnetic clutch, AC compressor was running fine and system was cooling just fine. So my next step would be getting some LM321 op amps ...
How long did it take you to open all coverings to get access to the AC amplifier connector? "
Hi As you mention,, i am definitely interested in this smart fix,, can you pls send me more information regarding this,, the step by step instruction you listed,,
1. Get Techstream cable/software from Amazon/ebay and connect to your car to verify the problem (i.e. flow sensor output below 3.8 V and that the cooling system works when the compressor is manually engaged) Which model number?
2. Remove the glovebox to gain access to the A/C computer (there are many steps involved, including removing the SRS knee airbag on the passenger side) Any pictures you still have?
3. Design a non-inverting operational amplifier (this is easier than you think, check wikipedia article on operational amplifier). Can you send me design,, is it same as one of your posts?
4. Insert the amplifier between the compressor flow sensor and A/C computer. The amplifier power supply and ground should use the same ones as the flow sensor (pin 30 for power and pin13 for ground on the AC computer). The flow sensor voltage is fed to pin 7. you'll have to cut this line to insert the amplifier. Any pictures with you and , so i suppose we only access the ac computer and not go near the actual compressor itself?
5. enjoy your A/C go spend $2000 somewhere else! Thanks again,
Just rigged up an AC flow sensor boost circuit using IC 741 op amp (instead of LM321 op amp), bench tested it, corrected one mistake, then installed in my 10RX .... works great, my AC system is cooling again ....
Here is my experience:
- The hardest part was to install the TechStream sw on to my 64-bit Win7 laptop, search Youtube for complete instruction ...
- In my 10RX, the AC amplifier is located to the right of the cabin air filter (located behind a door in the back of the glove compartment) ... and I could easily unplug the big F50 connector, locate the 3 wires needed to feed to my booster circuit ... a picture is worth a thousand words, so here are some pictures
- took about 20 mins to build the booster circuit, 10 mins to install it in my 10RX .... 30 mins total, saving about $2000 ... best feeling ever
I just replied to your latest post with pics, somehow its gone. Thank s again, i had a few questions on my reply.
Any recommendations on the techstream cable/sw brand or model, where do i hook up the techstream ?
So the make the booster , need an 8 wire cable.
pictures 1,2, are reading or data prior to connecting booster fixture.and engine on?
pic 3, data during test, booster installed,engine on, ac on
pic 4, data after 3 minutes of test, booster installed engine on, ac on
pic 5, f50 connector(this is where the booster wires are to be connected), connector view of D10 is for reference only.
pic 6, spec table for a normal flow sensor
pic 7, location where the f50 harness is, inside or behind glove compartment, do not touch other harness bundle on the left
pic 8 schematic of booster
pic 9 wiring diagram of booster complete with materials cable and pcb
pic 10 a finished booster prior to connecting f50 harness connector
pic 11 unpluged view of f50 connector showing wires or pin location to connect wire from booster
pic 12 actual connection of booster to f50 harness, soldered terminations, follow wiring diagram
pic 13re bundled up booster and f50,, and replugged f50 to ac computer.
sorry for my ignorance, for those other inquiries, your information is a huge help. thanks again
05-27-16, 08:22 AM
RX350 2010/2011 Air conditioning DTC B1479 cheap solution
