Serial A/C to normal A/C request

[SkinnyPedal]

This is for a customer having issues with a swap they did. They used a 2005 5.3 from a Silverado, OS 12592618. I know that system uses pressure sensor and low pressure switch going to the AC unit then requests over serial.

Anyone know if there is a way to switch a 1 meg blue green ecm from Serial AC request to switched request like the red blue ecm?

Is it easiest to tune it as a 04-05 express van that already has ac switches and a normal 12v request?

[schwoch1]

I had the same problem a while back. I swapped an '04 5.3 out of a Silverado into my '71 GMC. No matter what I did I could not get the A/C to work with the 12V input like the S10's and the vans did of the same years. What I found is that they used 2 PCM's in that year, one for the Silverado's with serial data engaged A/C, and another PCM for the vehicles that did not use serial data to run the A/C. After I swapped the original PCM (12586242) to a 12586243 PCM the A/C worked fine after wiring it like an S10. I was able to flash the Silverado tune into the S10 computer fine (although EFI Live did catch it and warn me!) and have been driving the truck for over a year with no problems. It looks as if the '05 Vans wen to serial data A/C, so if I had the vehicle here, I would just swap in the '04 PCM and flash an '04 tune into it and get your A/C control working again. Hope this helps!
Mike

[Taz]

Hello Mike,

I recall your A/C Type thread - you and Brendan did a great job sorting things out.

Just some clarification - the A/C activation on the Gen III Express / Savana vans never changed throughout their production run.


Cheers,
Taz

[schwoch1]

Hello Mike,

I recall your A/C Type thread - you and Brendan did a great job sorting things out.

Just some clarification - the A/C activation on the Gen III Express / Savana vans never changed throughout their production run

Cheers,
Taz

You are right Taz, I just checked, sorry about that. So with that said, did the express/savana twins use a different PCM than the Silverado/Sierra's did?

Mike

[Taz]

... did the express/savana twins use a different PCM than the Silverado/Sierra's did? ..

Gen III engines - Yes sir, different PCM.

Silverado / Sierra with 4.3L V6 - same PCM as Express / Savana.

[Big Mike]

I'm in the same boat. Swapping an 04 LQ4 6.0 from a 2500HD to an 87 K10. Obviously the original 12586242 PCM that came from the donor is looking for a serial data AC request and I need it to accept a 12+ batt request instead.

So to clarify this thread. The trick is to swap to the 12586243 PCM and then flash the original 04 tune into it, and it'll then look for the 12+ batt AC request instead of serial data?

The DBW and DBC difference between truck and van doesn't matter correct?

[Taz]

There are two factors at play ... hardware and software. Switching PCMs addresses the hardware portion. If you need to use PCM ground (grounds a 12 volt source) to activate the A/C compressor, then you will need to run an Express / Savana tune, and also use the Low & High A/C Pressure Switches used by these vans.

Van tunes could be either DBC or DBW - so no issue there. If you use a mechanical fan, no worries - you are finished. The only difficulty you will face is if you also want to use E-Fans. For the PCM to activate E-Fans based on A/C pressure, you will need to use an A/C Pressure Sensor (not the Low & High switches) - which is not compatible with the van tune. This setup would require a custom tune.

[Big Mike]

Thanks for clearing the grey area TAZ, which was the hardware/software thing. I didn't think it was as simple as throwing the truck tune in a 243 PCM.

e-fans are a must for this build as at some point it's going to a COS5 in preparation for a turbo so I'll need all the real estate up front I can get.

I'm not as proficient on van tunes but it basically sounds like the vans remained just like the 99-02 F-cars were with their dedicated AC pressure sensor that controlled the fans. And if so, I can add the sensor and it's related wiring in no problem. Getting a 243 PCM is also no problem. What I could use assistance with is choosing a base DBW van tune that can go COS5 later.

Then I'll assume getting the fans working in the tune is basically like when adding e-fans to a 99-02 truck where you switch the auto recirc to #2 fan control and make the necessary changes in the fan control folder. Or is there a grey area there too I'm missing?

I've tuned stock platforms, truck mostly, this is just my first full fledged complete drivetrain swap.

[Taz]

... e-fans are a must for this build as at some point it's going to a COS5 in preparation for a turbo so I'll need all the real estate up front I can get ... I'll assume getting the fans working in the tune is basically like when adding e-fans to a 99-02 truck where you switch the auto recirc to #2 fan control and make the necessary changes in the fan control folder. Or is there a grey area there too I'm missing? ...

You are very welcome. You seem to have a good grasp of things, but the nuance of very special custom tune required does not appear to be fully understood.

A 1Mb van tune will allow the PCM to control the A/C Compressor via a ground - like the 1999 to 2002 512Kb trucks did. It will NOT work with an A/C Pressure Sensor, and therefore will NOT activate the E-Fans based on A/C pressure.

A 1Mb truck tune will work with an A/C Pressure Sensor and will activate the E-Fans based on A/C pressure. It will NOT activate the A/C compressor via a ground (it is setup for Serial Data activation).

Your choice is to either run a van tune and a mechanical fan (or non-PCM controlled E-Fan), or to run a truck tune that has been modified for A/C compressor ground activation, which will support E-Fan operation via A/C pressure.

If you absolutely need to control E-Fans based on A/C pressure - then you are looking at purchasing a custom tune. Neither HPT nor EFILive have these parameters.

[Big Mike]

Now I got it. The van simply isn't capable of controlling the e-fans for AC operation even with an added AC pressure sensor. I was under the impression they would IF a pressure sensor was added. Shows my lack of van experience and I should also include the guy who told me it would work in that lack of experience too.