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Discussion Starter #1
Is there anyway to wireup the ac system to an infinity ecu and bypass stock ecu?
 

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You mean totally ditch the stock ecu? I’m not sure you can easily delete the stock ecu and keep the AC. I’m sure there’s a way but I’ve never researched it. I remember some old posts where a guy had done it...seemed like they ran the AC switch straight to the compressor clutch and bypassed all the temperature and ecu stuff?

I’ve got my Infinity set up to sense when the radiator fans come on. They kick on when coolant temp > 205F but they also kick on when you run the AC. The Infinity will bump idle rpm up to compensate for the electric drag of the fans running. It’s not as smooth as stock but damn close. I’m using the Infinity to control the stock ETCS-I DBW throttle body, though. I’m sure similar could be done via an IACV if you’re not DBW.
 

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Yea the climate control system is pretty complex in operation. It takes various readings from multiple sensors. MPX and ECU will control it. That’s why it doesn’t work with the stand alone as you have figured out. You might be able to get an ECU pinout and try and mimic certain readings to fool the stock climate control into working. That’s probably a long shot.

You could manually apply power to the compressor via a toggle switch, but if for some reason the pressure reads to high or to low (leaking system) then you will burn up the compressor and not even know it.
 

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Not an infinity system but I have my car setup with a megasquirt3x. It is running the car standalone with no factory ecu. To keep the ac working and still use the ac controller. I modified the control panel to have an output for when the ac is turned on. I feed that signal to the ms3x and use an output from the ecu to control the ac magnetic clutch relay. But before the relay, I run the signal through the dual pressure switch and then to the relay so I still have safety incase I develop a refrigerant leak I won't burn up my compressor. And the ecu knows when I'm running the air and bumps up idle to compensate.

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Discussion Starter #5
Thanks for all the replies. I will try ExtremeFam2007's way and see.
 
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@ExtremeFam2007

Do you have a pic or diagram of how you wired the thing up yet still retained the safety features? Would be interesting and helpful to future viewers of this post to see how you did it.

Not to detail the thread, but I am guessing you’re using a digital dash since you excised the stock ecu?
 

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@ExtremeFam2007

Do you have a pic or diagram of how you wired the thing up yet still retained the safety features? Would be interesting and helpful to future viewers of this post to see how you did it.

Not to detail the thread, but I am guessing you’re using a digital dash since you excised the stock ecu?
No diagram from me but the switches are normally closed if working correctly. Meaning power is being transferred through them. Just ground a switch on one leg and provide power to the other leg. However instead of powering the switch directly from 12v source you run that leg through both low and high pressure switches and then to the switch. That way if something was to happen pressure wise a switch will “open” and thus cut power to the switch.
 

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Well, kind of. . . It's a dual pressure switch. One brakes contact if the pressure is to low. And another breaks contact if it's too high, they are in series together. You don't have to power anything. The AC relay, like most things are always powered and you're simply controlling the ground side of the coil in the relay. I deleted the factory ECU along with all the extra additional plugs that aren't being used. I just looked at the schematics and ran my wire I'm using for the AC clutch from the standalone into the wire going to the dual pressure switch and then the wire coming out of the switch to the wire going to the relay. I also added diodes to the fan relay to replicate what the factory does. So when my standalone calls for ac the clutch engages and the cooling fans turn on low.

I am also still using the factory cluster. The only thing I have lost is my coolant and instant mpg gauge. I am in the process of bringing those two back to life as well. I plan on modifying the cluster so I can drive those two gauges with the standalone ecu using pwm. I've even thought about changing the mpg gauge to work as a factory boost gauge like in the sw20 MR2. The only thing that's held me up is not wanting to mod my factory cluster as I've really been eyeing one of the cluster the with tach in the center.

The only thing I've lost with the factory ecu that I haven't been able to get back so far is the outside temp reading beside the clock.

Also keep in mind that it is a manual car. Different story for the auto.


I'll have a look at the spreadsheet I made and see if I noted the colors of the pressure switch wires in the case of could help anyone.

Oh and btw I do use a digital dash of sorts as well. I've gutted a factory nav unit and put an HD screen with a Rpi4 running it. The kids love it as it functions as a digital dash when I want and an entertainment center when the kids are in the car.

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Man that was informative. I don’t think I will ever delete my factory ecu, but I feel more confident in doing it now. It is a real wiring mess in the ecu box between the stock ecu and the Infinity wires. I did it very clean and loomed everything and used deutsch connectors but the sheer amount of wiring makes it hard to be neat. You’ll have to make a thread and post some pics if you feel like it. I’d like to see the raspberry pi displaying data. I have a PerfectTuning Canbus gauge in a custom cluster bezel, it’s nice but I wish it was bigger display. My factory cluster works but when I get past about 8psi the insta mpg pegs “80”. I gave up simulating all the factory signals since we do not have emissions here. I am surprised your fuel gauge works. I always thought it relied on a calculation derived from the MAF, igniter, and stock ecu, and would move in 1/4 tank (incorrect) increments if everything wasn’t satisfactory to the stock ecu.
 

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My fuel gauge is a little funny at the moment. It always worked fine except the fuel light would stay on. I simply removed the bulb. But after my last trip in the tank my fuel gauge doesn't go below about 3/8th of a tank. And I believe I just have fuel line from the jet pump mess in the way. . .

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Did some looking at the ecu pinout. A25 “PRE” is the Dual pressure switch wire. According to the pinout, it is a blue/yellow wire. So you would come from the “AC” button (can’t find the wire color for it) go through the MS3 input then lowside output to the dual pressure switch and terminate at the AC clutch relay (-)12V coil side? Pretty intuitive to wire it that way man.

Yeah the fuel gauge is voodoo on these things. Don’t know how true it is but I’ve read Lexus didn’t want the gauge to fluctuate based on the car’s plane of incline/decline. So instead of just using the float to display actual fuel amount, it has this calculated via the MAF, and ignition, and distance traveled. It uses the float as a backup. I know for a fact there isn’t a low level sensor in the fuel sender. That’s what is used to turn on the low fuel light in every other car/bike/tractor I’ve worked on. It’s a scary thought but current is passed through a thermister. As long as it‘s submerged the thermister remains cooled by the fuel but when the level drops, the current heats the thermister and closes the circuit and turns on the low fuel light.

fuel gauge .... always worked fine except the fuel light would stay on.
I have no idea what turns on the low fuel light in the IS but I am guessing the dual floats or a calculation? But if yours always stayed on yet the gauge worked via the float then I don’t know. Voodoo.
 

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You won't find a wire color code for the AC button as it doesn't exist. That's what is normally communicated over the mpx signal in Toyotas BEAN language. That is the worst part of retaining the AC function without factory ECU. What I personally did was modified the climate control unit so I have a wire coming out for the AC button now.

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It’s a scary thought but current is passed through a thermister. As long as it‘s submerged the thermister remains cooled by the fuel but when the level drops, the current heats the thermister and closes the circuit and turns on the low fuel light.
Yeah i read about that, and being a mechanical guy not and electrical i thought that sounded like an accident waiting to happen. Still, how often do you hear of it being a problem? None that i know of... well not in Toyota/Lexus anyway :sneaky:
 
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