eng1nerd

iTrader: (2)

I'm wrapping up all the wiring on my Lexus IS300 LS1 swap and am trying to figure out the A/C. My big question is if the GM PCM gets a compressor status signal can it adjust idle without ever seeing an A/C request signal or pressure sensor?

My goal is to retain the factory Lexus climate control features and some of this is handled in the ECU (which I am keeping hooked up). I am planning on letting the Lexus run the compressor (LS1) and all the original (Lexus) sensors. I don't know enough about the way the LS PCM handles A/C to know if I can do this or if it needs to control everything based on the input signal.

Any help would be greatly appreciated. I live in "Hot"lanta so cold air is a must.

rigid

iTrader: (5)

Could you use the factory IS controls to give the GM ecu the 12v signal? As in use whichever wire engages the IS compressor send that to the gm ecu. Exactly which features on the IS are you trying to keep?

garys 68

iTrader: (1)

I've got 2 swaps, 6.0 LQ9 with Vintage Air, 5.3 L59 with Classic Auto air. Both with Sanden compressors. No AC request signal, no changes in cam, engine, or tune. No problems.

bczee

iTrader: (12)

I have no AC Request Singal to the PCM on my Chevelle.. I have a manual trans.. I can feel the engine RPM dropping RPM sometimes, depending now how I come to a stop (quickly or smoothly).

It would be more of an issue if it was a Auto trans. But depending on the Tune. It can be ok, but if you can hook the signal up. It would help.

ls1nova71

iTrader: (4)

the A/C request is it really needed the PCM will adjust the idle for any load put on the engine.

eng1nerd

iTrader: (2)

I figured the would compensate but didn't know if having that much load, that sudden would be problematic. The car only has an 18 lb flywheel too so I'm sure that won't help the idle drop any either.

68lsxc10

iTrader: (1)

Most of the swaps I have done, you couldn't tell when the compressor comes on. Engine compensates just fine. I did however hook up the vintage air on my Chevy II and have the ecm control everything without the pressure sensor. I looked up the voltage range that the sensor outputs during normal pressure. I then built a small adjustable voltage regulator, dialed to the middle of this range and the ecm thinks the pressures are fine. I wired it in so that the pressure switch would interupt the signal to the ecm and the ecm does the rest. I know I'm opening a can of worms because you are gonna ask for more details and its been so long since I did it that I don't remember the values at all. I will look and see if I can find the schematic that I drew out. But it can be done without a pressure switch.

69 Ghost

It helps to know which PCM you are running and how the control panel works assuming that it just sends out a 12v signal. If you running the earlier style PCM you should be able to set it up properly. I am running a 04 GTO OS on a 243 PCM using the 12 volt signal to the compressor to run the fans, etc. on a vintage air system soon to be a factory hybrid where the entire a/c portion will be modern in an original box using original controls. It can be done even if the wiring may show different as long as you have the programming tools on the PCM side.

eng1nerd

iTrader: (2)

Were you able to find the information you had on the voltage regulator or what the GM sensor needs to see to think there is pressure?

Now that the car is road worthy and it is +90 degrees here I need to start working on the A/C setup.

ls1nova71

iTrader: (4)

Why do you want to go to all the trouble of having the PCM control the A/C just to fake it out? The PCM controlls it based on pressures. On the older PCM's you can just hook the A/C request up to the compressor circuit to control the fans, but it appears you're using a PCM with out the request. What year and OS ao PCM are you running?