AC Request

[NC_John]

Originally Posted by 87chevy.com

is this a 2002 and lower pcm? If yes, 12v to the ecu is will then the compressor on if the pressure high pressure switch is installed.. Or of the signal wire is grounded.

If it's the 03 and newer think that's can bus and for some reason the aftermarket is being lame on solutions.
Clint

04.

[indymachinist]

There are 3 main reasons to let the PCM "control" the a/c. 1) the PCM can turn the fans on and off with the a/c 2) the PCM can kick up the idle when the a/c clutch is engaged 3) the PCM can turn off the a/c clutch at high load/high RPM

[First c10]

Originally Posted by indymachinist

There are 3 main reasons to let the PCM "control" the a/c. 1) the PCM can turn the fans on and off with the a/c 2) the PCM can kick up the idle when the a/c clutch is engaged 3) the PCM can turn off the a/c clutch at high load/high RPM

Correct but the problem is finding a way to inform the PCM the AC has been turned on.

[orngsikL]

BP automotive says it's possible.
Still trying to figure this one out.

[chebyshortbox65]

It’s possible I’ve been running a blue/green ecm for over 4 years with the pcm controlling the a/c compressor and fans. The programming has to be set up for it with hp tuners pin 17 blue connector 12v through high pressure switch. Pin 43 blue connector to a/c clutch relay to ground the relay. Pin 55 green ground through the low pressure switch. Pin 18 green connector 12v spliced in line with the compressor 12v supply from the relay output. Factory 03 up a/c transducer pin 1 transducer to pin 80 blue connector. A/c transducer pin 2 to pin 45 blue connector. Transducer pin 3 to 14 green connector. It’s a mix of f-body. 99-02 and 03-06 wiring.

[Accelo]

I went through the same thought process. I have 2000 ECM so no canbus issues.
I was convinced the ECM could possible compensate for the air on idle issues if I had a air-condition demand on in the computer.
My original tune was alleged the stock tune. Turned out it had been messed with.
So I was concerned about my idle especially with the air-conditioning engaged.
With the air-conditioning engaged it flat out would not idle after it warmed up.
I had the cart before the horse. The tuner was able to get my system straightened out and it idles nicely even air-conditioning engaged.
The ECM requests an idle speed and varies the outputs to achieve the designated idle speed. So it should be able to compensate for variable loads like high alternator output or air loading.
My motor is maybe a 50 rpm higher than stock as it pushes slightly coming to a stop.
My system is working and has decent drive-ability with out an air-conditioning request to the ECM.
I am using a BTR Stage II truck camshaft in a LS1. If you have more cam and/or less displacement I understand how this may be difficult.
I had a goal to use the stock converter and frankly I wish I would have changed it. For the off the line grunt and the idling pushing issue.
Wishing you progress in getting this issue resolved.
Cheers

[Rust-O-Matic]

Originally Posted by chebyshortbox65

It’s possible I’ve been running a blue/green ecm for over 4 years with the pcm controlling the a/c compressor and fans. The programming has to be set up for it with hp tuners pin 17 blue connector 12v through high pressure switch. Pin 43 blue connector to a/c clutch relay to ground the relay. Pin 55 green ground through the low pressure switch. Pin 18 green connector 12v spliced in line with the compressor 12v supply from the relay output. Factory 03 up a/c transducer pin 1 transducer to pin 80 blue connector. A/c transducer pin 2 to pin 45 blue connector. Transducer pin 3 to 14 green connector. It’s a mix of f-body. 99-02 and 03-06 wiring.

This is very interesting. Do you know what service number your pcm is? Do you have any idea exactly what was modified in the tune? Or how this works?

I'm trying to wrap my head around the wiring, because half of these pins aren't A/C related, and the link below shows that most blue/green pcms are missing the components required to recognize the 12v request signal. My understanding is that the BCM sent a serial data signal for the request in '03+ pcms, rather than the standard 12v request like '99-02.

Blue 17 = Signal B (A/T) Trans Fluid Pressure switch
Blue 43 = Fuel injector 7 control
Green 55 = Not used
Green 18 = Clutch start switch (M/T)
Blue 80 = Low reference (ECT)
Blue 45 = 5 volt reference (A/C)
Green 14 = AC refrigerant pressure sensor signal


For anyone who hasn't seen this thread yet, check it out:

https://ls1tech.com/forums/conversio...c-request.html

[orngsikL]

im using a E38 Gen 4 PCM.
still fighting this.
I know the transducer switch on the high side line is working and getting a 5v ref and sending out a voltage as related to the pressure, but I still can't get the ECM to read it with HP Tuners VCM scanner.

I have a segment swap done for the fans, just dont know if it's the right one. As this ECM originally came out of a Chevy Express 3500 with a clutch fan.

The fans are working correctly, controlling engine temps, but are not working to control ac head pressure / temps when the engine is under minimum coolant temp for the fans to come on and I blow the relief valve on the ac compressor.

[orngsikL]

GOT IT FIGURED OUT TODAY FOR GEN4 with a E38.

So, a little back ground.

The truck and van OS on a e38 used the canbus system, which used the ac control panel and the BCM to communicate with the ECM and tell it when the compressor is on and this tells the ECM to read the ac pressure transducer. Without the canbus and the BCM, it wont work on a truck / van OS.

Now, here's the solution and I got it working tonight:
E38 Camaro OS doesnt use a bcm or a canbus signal to tell the ECM to monitor the AC pressure transducer, it just reads it on it's own via a 5v ref pin on the J1 connector at the ECM, which goes straight to the AC pressure transducer and uses a ground via the switch and a return wire that sends the corresponding voltage back to the ECM. The ECM then converts this voltage to pressure and there is a table in HP Tuners under the fan section that allow you to set the electric cooling fans to come on with your programmed pressures. So you can do a Camaro OS swap, but it has to be compatible with the ECM hardware itself and with your TCM. Also you have to run a Camaro accelerator pedal for the camaro OS.

Mine is working perfect.
Shoot me a email if you need some help.
c10clubLA@gmail.com as I dont get on here much anymore to check the replies and PMs.

[67-C10]

The jeep guys use a canbus add on to enable the ac request. Ain't that cheap of an option but it does exist. http://www.rpmextreme.com/Product/23...st-Module.aspx
I got my engine from a van 2011 and kept the bcm. The van bcm will take a ground or 12v I forget which but generates the canbus signal to the ecm for ac on request. 03 up gen iii need the hvac module and the bcm to talk to the ecm I believe at least in the trucks and suvs that's the case.