G-Body

iTrader: (4)

Best I can tell serial or analog look for a pressure sensor input as all of those systems used the pressure sensor. If you set it to anything that has cycling in the name it disregards the pressure sensor and looks for the high and low pressure sensor inputs. The vehicles with green blue pcms and pressure switches always used a mechanical fan so I don't think gm put any programming in to turn on e fans in them

G-Body

iTrader: (4)

For anyone trying to switch from a pressure sensor based system to a pressure switch system (cycling system) this is very important.


I was trying to make my 6106 PCM work today and I was watching the tech 2. I had it set to analog cycling (was a serial PCM from the factory) and I noticed that when I requested the A/C it would show the request and show that it had normal pressure at the low pressure switch (had to watch it as if I was watching the data for a 4.3L G-van on the tech 2 or it would not show data for the low pressure switch), I noticed that it would turn the A/C comp relay on and bump the idle for a second or two right after I requested A/C but once it dropped out I had to restart the car to get it to work again.

Turns out all the PCM`s that used a pressure sensor from the factory have P0530 set to "no mil light" so if you try to switch the PCM to a cycling setup when you request A/C it checks for the pressure sensor output a couple seconds after starting the compressor....since there is none, it sets a soft code, and disables the a/c compressor thinking the system is under pressure. If you switch p0530 to "no error reported" you can get the PCM to enable the A/C relay and bump the idle. Not sure about the fans, motor was too warm by then to tell for sure.

TXjeepTJ

iTrader: (8)

Someone said to wire the Blue/Green DBW pcm as an older pcm (12 volts to green connector pin 17 and ground to pin 55) and just set it as "analog" using hptuners.

I did this, and I am still not getting anything

Running a 2005 PCM DBW blue/green, all I want to do it tell the PCM that the AC is on so it will bump up the idle.. I'm using a trinary switch to control the compressor and fans so the PCM controlling everything is not needed, I just want it to bump the idle when the AC comes on.

TXjeepTJ

iTrader: (8)

Well, got the resistor and followed G-body's directions. Still isn't working... switched between analog cycling and analog with no luck.

C1 pin 45 and C2 pin 14 are connected using 50K ohm resistor
C2 pin 17 getting 12 volts when I want AC on
I even grounded C2 pin 55
Looking through pinouts C2 pin 80 is a A/C pressure reference so I grounded that also, still nothing

I also disabled the P0530 code in the PCM

Don't know what else there is to do. . . . . .

TXjeepTJ

iTrader: (8)

How did you wire this up? Or did you use the actual sensor? Not sure how to wire it to make it think he has the correct pressure using resistors, since it uses 3 wires

ls1nova71

iTrader: (4)

I used the actual pressure sensor from the 2004 truck, but that wasn't the end all fix. As someone said earlier in this thread, only some PCM's have the capability to run the 12v A/C request. From what I gather, you need a PCM that has IAC drivers in it. Sounds crazy, but when you think about it, it isn't. When GM went to DBW in all pick ups in 2003, they took the IAC drivers out of most, but not all PCM's (probably to save a nickel ) and along with that, they must have taken out whatever is on the board that makes the 12v request work since that same year they switched to serial request in the PU's. That said, vans still were DBC, and also had 12v A/C request, so they must have all the hard parts still in the PCM. I actually tried the analog cycling and was giving the PCM 12v, but never worked until I swapped to the van PCM, works fine now. Hope this helps.

What is the service number of your PCM? I'm going to guess it's from a truck?

TXjeepTJ

iTrader: (8)

Ah yeah, I read that too - but figured it wasn't really confirmed true since it seemed like everyone was getting their AC to work.

I'll need to see what PCM I have, but it was off a truck that had DBW (I'm running DBW also)

So if I track down a 03+ blue/green pcm that came out of a van it will work with DBW or would I have to convert to DBC?

Thanks!!!!

ls1nova71

iTrader: (4)

I'm pretty sure all the blue/green PCM's will run DBW, it's just certain ones that will do both. I'm running DBW also. My actual PCM came from an S-10 Blazer, you just need to make sure you have the right service number.

TXjeepTJ

iTrader: (8)

Do you know which service number is the correct PCM? I have a friend with a V6 Silverado PCM that isn't being put to use. Wondering if that one would be work

TXjeepTJ

iTrader: (8)

Ok so I picked up the V6 PCM from a friend, which luckily enough I already have a HPtuner license for (so don't have to cough up $100 to tune it).

Service number is 12602801 which google/another ls1tech thread says is a 2007 Express, Drive by Wire, (has IAC drivers). So this should solve my problem hopefully.

One issue now though, can I flash my current tune onto this pcm straight up? The PCM came out of a V6/60E and my current tune is for a 6.0L/80E

TXjeepTJ

iTrader: (8)

The V6 PCM worked. All I had to do was ground pin 55 and apply 12 volts to pin 17 + change to cycling analog and it bumped the idle up. Thanks for the help everyone

ls1nova71

iTrader: (4)

Cool, glad you got it going! I checked that service number and you are right it has IAC drivers in it. I didn't think about the V6 trucks still being DBC until '07 or so.

branndonw

iTrader: (3)

Sorry for bumping an old thread but I've been searching and haven't seen anyone address this so here goes...

I have a 04 Extreme blazer 4.3L that uses a P59 (blue/green) pcm. It has an analog cycling AC system so it uses high and low pressure switches instead of a pressure sensor. I installed LS1 fans (3 relay) a couple years ago and the PCM controls them just fine based on ECT but won't command them on with AC due to the lack of a pressure sensor, so i just used a couple relays to make the fans come on with AC. I replaced the AC system a few weeks ago and while the system was down, I installed a pressure sensor. The high and low pressure switches are still installed and wired up appropriately. So my question is if I set the AC type to analog so that the PCM will monitor the pressure sensor instead of the switches, is that going to cause any problems when using a fixed compressor instead of a variable compressor?

jayyk31

iTrader: (2)

The fixed displacement compressor does not have the pressure control valve to regulate the displacement. I'm thinking you need a variable displacement ac compressor and also need to do a segment swap.
on the other hand I'm sure you can reverse that and cycle the clutch.on a variable compressor but not rhe way you have it.
unfortunately the PCM will not monitor the pressure transducer and control the fans with the s10 operating system. You have to segment swap the ac part of the tune (system) from a compatible operating system from a vehicle that uses the 3 wire pressure transducer from the factory. I believe you can use a vette tune just have to do some research to make sure. Most guys with the 0411 use a 99-02 f body tune.

branndonw

iTrader: (3)

The Blazer OS will monitor the pressure sensor when you change the AC type fitted from Analog Cycling to Analog. There is no need for a segment swap. I already have it working. The fans turn on and off like they are supposed to according to AC pressure. After the change I did a quick data log and the compressor never cycled, it stayed on the entire time. The air blew cold the entire time and AC pressure stayed right around 2.2v (not sure exactly what that translates to in psi), which is about the same as it was when set to cycling and the compressor was engaged.

The pressure sensor is installed on the high side. With the AC type set to Analog, the PCM no longer monitors the Low Pressure Switch Signal (I verified this by unplugging the low pressure switch connector and the compressor continued to run). Even though it seems to run fine, I'm not 100% comfortable running the fixed compressor constantly (I put 1500 miles a week on this truck) when not knowing what the low side pressure is and also knowing that the low pressure switch will no longer disengage the compressor.

I made a minor wiring change to utilize the low pressure switch. On the blazer, the AC request signal comes from the hvac control module, goes through the high pressure switch and then goes to PCM X2-17. The low pressure switch signal goes from PCM X2-55 through the low pressure switch and then to ground. I removed the AC request wire from PCM X2-17 and connected it to the low pressure switch. I then removed the low pressure switch signal wire in PCM X2-55 and inserted it into PCM X2-17 (AC Request Signal). This puts both the low and high pressure switches in series on the AC Request Signal wire so now when either of the two switches open, the AC request signal will be interrupted, which will cycle the compressor on and off. So now I have a fixed compressor that will still cycle while having the system set to non-cycling to monitor the pressure sensor and give me proper efan control.

69 Ghost

1. If you use the analog cycling (fixed compressor 12 volt ac request) you need to wire the grounds (through the pcm) so that the low cutout switch works but you could also run the low pressure cutout switch through the ac request side with the variable compressor setting. GM has done both for the low pressure cutout switch (inline with the ac request but not on newer cars). All LS motors use the ground through the pcm wire and programming to do this.
2. Analog (variable compressor 12 volt ac request) does not use the ground wire (from the low pressure cutout switch because there isn't one) to the PCM.
3. The pressure sensor was not used with a fixed compressor until around the 06 tahoe setups. This is because they also used a fixed compressor with electric fans (tahoe setup). The trucks and vans didn't use electric fans hence no pressure sensor instead there is a high pressure switch(and the electric fans are not turned on in the OS).
4. The low speed fan or fan 2 will come on regardless if you wire it like a fixed or variable compressor when the 12 volt ac request comes on (electric fans must be on in the OS program).
5. You will not get the high speed for the fan unless you use the sensor or wire it to do so. In this case it's the pressure sensor is used to control the high speed or fan 2. This is the case for all dual electric fan setups regardless of the compressor type.
6. If you run the pressure sensor you don't need the pressure switches to control the compressor for variable compressors the sensor will do the low, high cutouts and the high speed fan when needed but you should to change the sensor variable pressure settings on an OS with a variable compressor when converting to a fixed because the variable compressors to turn on the high speed fan (and you need to wire the low pressure cutout see 1).
7. In order to use the sensor you must have the P0530 on. If you are not using the sensor and try to get your ac to work and it comes on for 1 second and turns off it is because P0530 is turned on.
8. The red/green and blue/green pcms all work this way but a number of the blue/green pcms do not work because the IAC drivers and the ac request circuit is not there. An example is the 04 GTO used a 242 and 243 numbered pcm the 243 works the 242 does not. Express dbc PCM's all work.

branndonw

iTrader: (3)

I wasn't asking how to wire it up and make it work. I already have it working. I was asking if running a fixed compressor in non-cycling mode would cause any problems, but that's now irrelevant because I wired it through the low and high pressure switches.

This may be the case for other operating systems but not for my blazer OS. I have been running PCM controlled LS1 fans on it for a couple years now and it absolutely would not command either low or high speed fans on with AC request when setup for cycling mode. I had to use relays to get them to run with AC. I had to switch to non-cycling mode and add the pressure sensor to get fans to work with AC.

When running a variable compressor, yes, the pressure sensor is all that is needed, but the pressure sensor alone will not properly cycle a fixed compressor. Fixed compressors need to be cycled off when the low side pressure gets too low. The pressure sensor is installed on the high side. So when it's set up for non-cycling, the PCM is only monitoring the high side pressure via the pressure sensor signal and no longer monitoring the signal from the low pressure switch, which is installed on the low side, so the PCM no longer has any idea what the low side pressure is. That being said, if the PCM was set up for non-cycling, only monitoring the pressure sensor signal, and was to cycle the compressor off due to a low pressure signal, it would be because the high side pressure was too low (which would likely only happen from being low on freon), and not because the low side pressure was too low. The compressor would run continuously until the high side pressure dropped below the threshold. The pressure sensor will cycle a fixed compressor off for high pressure since it's installed on the high side, but it will not cycle a fixed compressor off due to low pressure on the low side.

Again, this may be the case on some other operating systems, but on my blazer OS, I have P0530 disabled, set to "no error reported" and everything works fine.

69 Ghost

1. The pressure sensor will work with a fixed. You need to change the variables. Use a low pressure switch. so it will cycle.
2. If the fans are not coming on with the ac request then something is going on.

You may need to check the tuning software some don't have all the tables needed. You can use the variable setting by just putting the low pressure switch inline on the power side. I have done both fixed and variable with and without a pressure sensor. The only thing you don't get if you don't use the sensor is the high speed fan.

branndonw

iTrader: (3)

Please explain how the pcm would know to switch off the compressor based on low side pressure when it is only monitoring a pressure sensor installed on the high side. How would it know what the low side pressure is???

F68

Hello friends, I got a 99-02 Camaro harness, --and the ac pressure lead was cut off at the harness, where does this lead plug into under the hood?


I looked near the drier on some gm vehicles there are no plugs.....?