autocomman

Ok, maybe we can get this in a sticky with the correct info. ive got an LQ4 from a 2004 truck, its got the blue/green connector ECU. This one is a DBW and normally used the HVAC headunit to control the compressor via serial data through the ECU. We all know that the usually tuners can change this to a simple 12v A/C request, and a variable/fixed compressor etc etc.

So the question is, what pins have to be changed on the ECU for
1. A/C request,
2. Compressor clutch control, and
3. Pressure sensor, and what sensor to use.

There is a lot of stuff out there for the red/blue connector ecu, but a lot of scattered info for the blue/green Lets see if we can get it all in one place. For both the red/blue and blue/green ECU's and have it easily acessible. Hard fast simple answer, this is what goes where

autocomman

I know the answer is in one of your heads....

aknovaman

iTrader: (7)

Same pins as red blue pcms. I suggest wiring it up line a express van with manual ac. Use the express van settings.

69 Ghost

If you want to use a variable compressor wire it like a 02 Camaro. If you want a fixed compressor wire it like a Express van. Both use a 12 volt A/C request. The programming portion only sets the A/C type. Also note that you can use a variable compressor on anything. The difference is a wiring and either a pressure sensor or switch.

bigmandengo

iTrader: (21)

I'm trying to figure out how to make a pressure sensor and a 12v request work on the green/blue ecms. Are you saying you have this figured out? It seems to me its a matter of being able to program the ecm this way.

autocomman

Wire the sensor like a van then? And get a sensor from a van? is that a binary (only low or high pressure) or trinary (both high and low) switch? Or is it a variable sensor.

ls1nova71

iTrader: (4)

Vans use pressures switches, a high side and a low side, I would think that would be the way to go. They are the same as the older trucks with the blue/red PCMs in terms of how its wired. The real question is what gets changed in the tune.

bigmandengo

iTrader: (21)

The van does not use a pressure sensor, it uses a cycling switch and a high pressure cutout switch. The reason I want to use the sensor is so the electric fans function properly. The van programming does not control the electric fans with ac, however the 03-06 trucks do, but they don't have a 12v request.

I've heard bp automotive can make the 12v request and the pressure sensor work together. I own hptuners and built my own harness, so I'd like to figure out how we can do this on our own.

autocomman

Ok so then this diagram is for an 02 Fbody, this cannot be used with a fixed compressor? Because ive seen people do it, there is even a thread or 2 in here that used this. If you wanted fan control can you do it this way?

THe second diagram is the express setup, very simple. High pressure cutout inline with the A/C request. Compressor clutch control, and the low pressure switch looks like its a ground signal for cycling control.

With that said, what in HP tuners gets changed. Is it that obvious? Im gettin my ECU flashed tonight at a buddys house and Id like to have that all straightened away.

2002 F-body


2004 EXPRESS VAN

bigmandengo

iTrader: (21)

Select Analog cycling in hptuners. This is a factory calibration from a 2005 express and this is the option selected.

69 Ghost

If the OS does not have 2 fans then you have to program it for 2 fans and wire it again like an 02 Camaro or a similar 2 fan setup. All 411 and Red/Green wiring is basically the same minus variations in configurations such as O2 sensors, fans, A/C, etc. All can be programmed to function like something else or a different OS can be used. If you at using a cable a 04 GTO or 05 Express van is a good start. If you are using DBW then a 04 Vette or 05 CTSV is a good start for car tunes. It is the combination of the 2 -wiring and OS programming that gets you what you want.

autocomman

Is this info in a sticky? Mods, can we put this stuff in a sticky somewhere? This A/C question goes by all the time it would be good to get it all in one place

mikesimpalass

I want to make sure I understand this, the 04 express van calibration uses a 12v signal for the AC request? But the express van calibration won't control the fans?

ls1nova71

iTrader: (4)

Yep, thats pretty much it. The worst part is the Express van OS are not DBW, at least ive never seen one.

Andy1

Perhaps it was my misunderstanding, but I thought the 01 Fbody AC unit sent a ground signal to the PCM C2, pin 17, but what I read here, the AC unit sends a +12V signal. Can someone please set me straight; is it ground, or is it +12V to C2, 17?
Thanks,
Andy1

69 Ghost

Guys please read what I said in my prevous post. An Express van or truck do not use 2 fans. Dual fans can be programmed to work through the OS. It can get confusing when trying to compare wiring diagrams and OS's but the general rule is if one setup has something -ie dual fans, variable compressor, 12 volt A/C request, etc it can be wired as such and programmed to work through the operating system. You must do both. I am running a 04 GTO OS through a 98 harness repinned as a 02 411 Camaro. Dual fans controlled by the PCM. 12 volt A/C request controlled by the PCM. Variable compressor controlled by the PCM. GTO's use the BCM to turn on the second fan and the compressor. Everybody says you cannot do what I did because they do not see it in their wiring diagram. All the red/green and blue PCM's work this way.

The request is 12 volts.

kleyba

Hi All this is a great topic I'm working on the same problem.

I've come up with these solutions for Blue/Green Connectors

On the left would require reprogramming with HPTuners not sure this is possible anybody can give me some input on this?

The option on the right would make the AC work independently not sure if it would affect the engine performance.

Thanks!

autocomman

Some poeple say when you dont tel the ECU the A/C is on their car runs fine. Really though with the A/C request hooked up properly, at near WOT the A/C kicks out, you can also set it to turn off over a certain RPM, the ECU also ups the idle, and can control fans if need be...so reconfiguring the ECU and hooking up proper A/C request and compressor control is the correct way to do it, but guys have gone around that.

WS6HUMMER

iTrader: (19)

Sorry to dig up such an old thread but I'm having issues getting the IAC to respond to the request signal on a swapped car. The OS is a 2001 suburban, its in an 89 caprice. I have the 12V signal coming from the pressure switch/sensor & have verified voltage to pin 17 but still the computer acts like it doesn't recognize the request signal. The compressor is set to analog cycling, does this need to be changed?

I'm not trying to operate the fans or anything fancy, just keep the car running when the ac is engaged.


Edit: I didn't ground C2 pin 55, is this needed?

autocomman

Im wondering that same thing WS6hummer, i finally got to the ac this weekend. Got the request hooked up properly, verified A/C request on a scanner, but it wont turn the relay on. I have the pressure sensor hooked up and it was a hot day, 111 psi, should be more nad sufficent to kick the compressor on, but wouldnt do it. Its a stock 03 silverado 6.0 OS, but with electric fans enabled and analog compressor control fixed compressor etc etc. Does the low pressure switch wire need to be grounded? on pin 55??

Mark