branndonw

iTrader: (3)

The AC refrigerant pressure sensor is on the line that goes between the condenser and the evaporator. The pressure sensor connector is #18 in the diagram.

F68

OK thank you for that info

Deanfe

Hello everyone, reading through all of this does get confusing. I am at the point where I am finally trying to get all of my wiring where it needs to be. I have a drivetrain out of a 2005 Denali, DBW, it uses a 12589463 PCM, it originally had dual electric fans and I am assuming the pressure sensor " my connector at the AC switch is a 3 wire". I am also installing a Vintage Air unit that I would like to integrate to the PCM just to have everything such as the fans, WOT, and idle bump to work. So is it possible for the PCM I have to do this using HPT to change the settings for the AC, it is also my understanding that my 9463 PCM doesn't have the IAC drivers, which it sounds is what I would ultimately need.

Thanks for any help!

ls1nova71

iTrader: (4)

If you don't have a PCM with the IAC drivers, then you won't be able to program it for the 12v A/C request. So unless you plan on using the truck A/C controls, it won't work. Also note that if you do switch to a PCM with the drivers in it, you may lose the fan control ability. Its not a perfect world....

Deanfe

Thanks LS1Nova71, that is what I was thinking from doing all the research that I have seen. Do you happen to know if I do wire in the AC pressure sensor if that will still communicate with the PCM regarding bumping the idle or turning fans just based on pressure from operating the AC system? I wasn't sure how any of that happens as far as where those signals may come from.

ls1nova71

iTrader: (4)

Sorry, but I don't know. I have never personally tried just wiring in the sensor alone so not sure if that will bump the idle or turn on the fans.

pdxmotorhead

I don't have the issue in my project.. (Megasquirt) but If everything but the fans is working, why not just use 2 relays, one driven off the AC compressor wire to turn the fans on when the AC is on, and a connection to a stand alone temp switch to turn the fans on if the temp hits 195? I know doing it all fancy with the ECU is the ideal goal, but it seems like a lot effort for a fan .. Or is this that common with the factory ECU(s)?

autocomman

I ran the fans through the ECU. And the main reason for running the pressure sensor in the first place is to have full ECU control over the compressor. Idle up, WOT cutout, high RPM cutout, and with that you can set the pressure at which the fans will turn on and off, and the ECU turns the fans off at above xx MPH, cause well they can be more of an issue than a help at 60mph. Having it all there already it was no brainier to have it control the fans for the A/C also. I could have wired around the ECU completely, but i prefer to have all the features of running it through the ECU. Especially cause this car has the old R4 compressor, and they dont like high rpms...eventually im gonna dump it for a Sanden...but still.

An alternative is to use a trinary switch like vintage air sells, kicks the fans on at 250 psi and off at 200 or 210 I think. Works great, and since you have air moving through the condenser at highways speeds the pressure is low enough it wont turn the fans on anyway. 12 ways to do it, no one is right or wrong, but in this case I wanted OEM function. Its worked flawlessly since

xEtherealx

I'm planning to use a trinary switch to disable my compressor and turn the fans on based on pressure, and activate the A/C clutch directly from the VA unit.

I'd like to have the ECU bump up idle when the compressor is active, cut it off at high RPM, and also turn the fans off at highway speeds. What ECU input pins do I need to set up achieve this? What I've read talks about getting the ECU to *request* the compressor clutch but since I'm controlling that externally, I only really care about these other features.


Based on my understanding:
- Pin 17 on the Green PCM connector fields A/C request, so I can connect the output/request of my aftermarket a/c system to this
- Pin 43 controls the compressor clutch
- Pin 55 senses system pressure via 0-5v signal
- I'll peg this to 2.5v in order to fool the PCM into thinking our pressure is nominal, since I'm using a trinary switch for regulation

The pinout at [1] has 17 and 55 unused though; will modifying the request type to analog in hptuners activate those pins?

[1] http://lt1swap.com/2004vortec_pcm.htm

xEtherealx

My wiring should look something like this

turbociv910

iTrader: (2)

I have a 2005 gmc sierra 1500 originally with a v6. I have swapped a 5.3 with a 2003 harness and pcm. AC compressor will not turn on, but will in the vcm scanner. Is this a tune or hardware issue?

rpturbo

iTrader: (47)

If you can force it on with the scanner, it's probably a tune issue.

autocomman

SO I dont know what hapend here, but ill restate the original thread topic and what I got to work, cause I feel like we are way off the deep end here. We all know the later trucks 2003 and up use serial data for the A/C request. I have a 2003 silverado 2500HD LQ4 6.0 with its matching ECU. I had the OS changed to a 2003 1500 SS which has the identical drivetrain for smog reasons (2 cats vs 4 for the HD). I had the A/C working both ways on both OS versions. The original Olds uses a cyceling switch on the accumulator. This is my 12v request into C2 pin 17. I retained the 2005 pressure SENSOR as well, not a switch. This allowed me to cycle the fans via pressure set in the ECU. I run a single 2 speed fan, with no issues from the STOCK OS.

C2 pin 17 12v A/C request.
C2 Pin 55 is grounded, this would normally be for a low pressure cut off switch.
C2 Pin 43 is the A/C clutch relay control.

Compressir control changed from serial to analog, not analog cyceling, one works, the other does not.
Fan pressure set to something like low at 190 high at 240 PSI? I cant remember off the top of my head.
Fan off at vehicle speed changed to 50 or 60mph

Thats it, there was nothing crazy or special my tuner did to make it work, I was standing there while the changes were made. It was easy, no issues. ECU controls the fans and the A/C compresssor completly on a STOCK ruck ecu that originally usd serial data from an HVAC module. I wired it like a van, but retained the pressure sensor. Its all detailed out. Simple and easy. Id love to know how this got to be such a mess for others.

If I remember correctly you can also set an A/C off high pressure point, which means you NEED the pressure sensor. You can also disable the A/C over a certain throttle %. I retained the pressure sensor and grounded pin 55. I dont think you can delete the pressure SENSOR you must retain that, set it to analog, NOT analog cyceling and ground pin 55. Done and done.

jayyk31

iTrader: (2)

The trouble is with the van OS's which are a 12v+ ac request. They dont use the 3 wire pressure transducer. They have a CCOT ac system and use a high press switch and a clutch cycling switch. Stock the vans have a mechanical fan. The Silverados, like the OS your using, can control the fans because they use the same ac system as an 4th genf body with the exception of the ac request. They have the 3 wire sensor in the high side, which GM uses to control the fans.

autocomman

Ok thats understandable, but I thought even the vans had control over a high speed fan output. Reguardless compressor control should work with the non van OS if you dont delete the pressure transducer, and you can set up fans with a separate trinary switch which is easy if you have a fitting put in the high pressure line. Have the trinary switch tie into the ground trigger for the fans, done and done.

350SS

iTrader: (38)

autocomman, do you know the part number on your ecm? wondering which it is, with iac drivers or not... thanks for posting your info, sure it will help others

autocomman

Its a blue green connector ECU, I dont remember the part number, Ill try to get it this weekend. Its a DBW car with the seperate TAC module if that helps, but Ill try to get the part number this weekend

350SS

iTrader: (38)

cool, thanks...just curious if it matches up with the has/doesn't have iac driver stuff posted lately
confusing subject to say the least

69 Ghost

You are taking this out of context. The pressure sensor only controls the low pressure to turn it on when using a variable compressor as stated. I never said it controlled cycling. In fact I said variables do not cycle and you need the low pressure switch to cycle. On variables with no pressure (the low pressure setting) and the compressor doesn't come on so it doesn't burn it up. Understand that the pressure will equalize (low side=high side) in the system when it is off so it has to have a minimum pressure to turn on the compressor.

If you don't use a low pressure cutout with a fixed compressor like you didn't then it will not cycle and you may freeze the evaporator. Chances are it will not burn up the compressor but you might without one. When it cools down enough and you start using the defroster you may have problems.

Your fans will not work unless you program and wire properly. I can only guess how you wired your fans and your programming especially if you say that you had to use relays to get it to work. Your OS was not programmed for fans. If you didn't turn the fans on in the OS then they woun't work.

Wiring is the same across the OS's for the fans and compressors with some minor exceptions like the 04 GTO where the fan is controlled by the bcm based on the compressor and fan type. Wiring for fan 1 is fan 1, fan 2 is fan 2, ac request is ac request, etc across all platforms. Again wire and program based on compressor type. Wire and program based on fan(s) type. You can't do one without the other and expect it to work.

autocomman

You got it 69Ghost, I did nothing special in my setup. The factory low pressure cyceling switch orignial to my oldsmobile is still in the accumulator and it supplys the A/C request signal to the ECU. Mde the most sense as this was origuinally the switch that cyceled the compressor directly. Pressure transducer hooked up as it was in the truck to supply high side pressure for control over the fans, and Pin 55 grounded. OS setup to Analog for compressor control, fan MAX MPH set to 50mph and pressures for high and low set accordingly. WOT compressor cut off I think I set at 80%. That was it, its a stock 2500HD drivetrain with a stock tune, no modifications at all other than turning VATS off. Even after setting it up as a 1500ss for smog reasons, the tune is unmodified, and I would venture to say the OS may even be the same. No issues making the A/C work. You must retain the pressure transducer, ground pin 55 and feed it your 12v A/C request, set the OS accordingly and it just works.