Yeah I didn't know if you had the A/C going in it maybe. That's right, there's nothing coming from the A/C wire from the a/c control unit in the dash. If I run 12v to the wire then the ECU turns the a/c on no problem.

I would trigger it right off the switch but that's internal to the control unit, there are no wires that go to it.

I could hook up a toggle to it but that's not fixing the problem so I'm not going to do that.

-Doc

 

I found my problem and nice cold ac again
All i needed to do is plug back in the heater control valve and wala it works. I deleted it not thinking i would need it but after searching on the forums found out it would be constant hot air and the ac would not work. I have the gte aem ecu and the settings in that are untouched for a supra application, ac/options/pr pressure low output ls6
I thought i needed to change it to the ge lexus version which had the pr-pressure low set to output gnd #6. But nope.

Sorry to the guys who don't have an aem

 

Hmmm, interesting.

 

So does anyone have working a/c with the stock ECU?

-Doc

 

I'm pretty sure I've got a definite fix for this, stay tuned.

-Doc

 

Toggle switch here. Didn't feel like tracing all kinds of nonsense out, just flip on a second switch to turn on the A/C. Doesn't bother me!

 

The early Lexus AC is control by the engine ECU and it send a ground signal (a small black wire with white strip) to the LCD display. Toyota ECU is little different and the AC is not getting signal from the LCD Climate control. Therefore you have to get a signal from the ECU to the LCD Climate Control Unit and from there the AC will work.

 

Yes, exactly. The only thing is that a normal relay can't be used, I have a few different relays of a higher sensitivity on the way and I'm going to try them, if that works then we're in business

-Doc

 

Doc,

You dont need that. All you need to do is to test the ecu output for a negative when KEY ON. Once u find that wire, then u are in biz. There are plenty of wires that will have that function. You can do it without going to the ecu. Any KEY ON ground would work. From there, connect that to the LCD Climate control (the black with white strip wire mentioned).

 

Um.... no... the a/c control unit is what gives the signal to the engine ECU.

The problem is that the a/c signal wire from the a/c control module on the Lexus gives a ground signal instead of a 12v signal when the a/c button is pressed. The ECU is looking for a 12v signal. So I wired up a relay to reverse the circuit, but the amperage going through is so minute that it couldn't switch on a regular relay. I located a different type of relay and tried it yesterday, works PERFECTLY. Just like stock

IF YOU HAD A WIRING CONVERSION DONE BY ME AND THE A/C DOENS'T WORK: Call me at 404-474-4573 or email drtweak@phoenixtuning.com and I'll put one of these together for you along with instructions on how to wire it up.

-Doc

 

This is a SC400 problem only. Trying to help a friend.
The harness was done by someone & assembled by someone else in Fla.
The car is up here now. Went through the Entire harness/ conversion
& this is the LAST issue.

The A/C problem is exactly as doc described & a toggle switch to me is
not an option. Searched extensively 5 forums & no clear answer.

The output voltage from the climate head stays low A/C On/ Off. Must
be incredibly low amprage change. (Swapped heads & ECU's w/ my car
for test)

I need the answer now - PAYPAL ready for the confirmed fix info

 

Doc, you'll be getting my harnesses within the next month....i was emailing you back and forth a few morning ago, will this be something that you'll do to conversions from here on?

 

Bringing one back from the dead... Anyway, I understand how the a/c was fixed in this old thread but what about a swap involving a '98+ vvti Aristo motor going into a '98 SC300? My original SC ecu has the "AC" and "ACMG" pins but the Aristo ecu only has the "ACMG" pin for sending the ground signal to the a/c clutch. The gen2 Aristo seems to have done away with the simple "AC" on/off input pin to the ecu. Instead it has a separate a/c computer which communicates to the main ecu via multiplex and I'm guessing this now gives the turn on signal to the main ecu.

Anyone solved this problem or knows the signal the a/c computer gives to the main ecu to ground the "ACMG" pin? I've got factory wiring manuals for SC, GS and Aristo which have all been invaluable for this swap but none of them go into detail about the multiplex communication for the climate control or transmission functions which would be cool to figure out. Thanks for any help!

Phil

 

Thanks Doc, I'll email you later.

I was also just looking at the translated 2jzgte vvti wiring diagrams that are floating around the net which I think are from a Supra (attached).

Anyway, this diagram does show an "AC" pin on the ecu in the same place as my old SC ecu. I wonder if the later Aristo ecu has this functionality too but the "AC" pin (connector D, pin1) is just left empty because it uses the multiplex on a different pin to control the a/c?

Phil

 

you have to throw a resistor in the signal wire...........why wasnt this mentioned already? i thought that was common knowledge?