Can anyone tell me where I would hook my AC request wire coming from my switch in my 96 S10 Blazer to in this diagram. It looks like the computer uses serial data from the HVAC module in the donor 2005 suburban to signal the computer to energize the AC compressor clutch. The S10 doesn't have a serial data HVAC module. I want the computer to control the AC compressor so it will kick on fans and bump idle as well. I do not have the 96 computer in my s10. Thanks..

 

From looking at your schematic the computer uses a serial link between the HVAC control module and the PCM You will need to get the HVAC control module to make it work. You could splice your wire into the switch in the HVAC control module and mount it somewhere out of sight.

 

You need a class 2 signal, Thaniel is right on.

 

Thats the only way to make the computer control the AC huh. Damn. Well, Docs Blocks sent me the wrong fittings for hoses so I'm waiting on the right ones now anyways. Hope to have AC soon, its' getting hot and huuumid here in Arkansas. Thanks for the replies.

 

Resurrecting this thread-

I have the 2003+ truck PCM in my conversion, and I'm researching wiring for the AC. I'm hoping someone has had some experience with this issue since the posting in 2007

The old post concludes that the only way to run the AC using the PCM is to scab on a HVAC Control Module because it says the signal to the PCM to turn on the compressor is a Class 2 data signal.

But when I look at the diagram attached, it looks like the AC compressor signal is just 12V out of the HVAC module going through a low pressure switch

It looks like to me that the 12V AC demand wire from the donor car could be hooked to the compressor clutch via the low pressure switch and the PCM would control the compressor by switching the ground on and off.

Is the class 2 data signal there to turn the compressor on and off or just for data/diagnostics?

Anybody done this?

Phil

 

Hey, never got the AC wired up. I'm now putting the engine in my 68 C20. I think you can reprogram the PCM to a truck program instead of the suburban program and no module is required. If you do it like your saying, the PCM won't control the fans or idle. I don't think anyways. Thanks for ressurrecting this thread tho. It was fun putting 20k miles on engine in the S10 Blazer. Good luck with yours.

 

Well they dont really need to control the idle, as the PCM well detect a higher load on the engine and up the idle anyways, (from what ive read in other forum posts) And as far as the fans, im wiring mine in to a stand alone switch, so i can tell them when i want them on and off. Id like to be able to cool my engine down at the track with it off.

 

You are correct about the signal out of the HVAC module, it is 12V, but if you wired it the way you described, I believe you'll be bypassing the PCM so it's not going to control the compressor. The class 2 data signal is what turns the compressor on via the HVAC module, and as far as mounting the HVAC module somewhere out of sight, it would be hard to do because the module is the A/C control head/switch on the dash, not just some little black box. You would have to mount the whole switch under the dash and leave the A/C switch in the on position on it. It could probably be done though.

Now for the interesting part, I'm going to assume you're keeping the DBW, or else you could get a PCM from a 1999 to 2002 or have yours programmed for those years, add the wires for the DBC throttle body, and add the A/C request wire to your harness, because they had a normal request line rather than the serial data type request. That being said, if you want to keep the DBW, I know some SUV's had DBW starting in about 2000 that would also have the A/C request line. The problem then becomes a TAC module incompatibility problem, I think, but am not positive about it, so it may work.

Or, I was told that some 2004 Express vans had an option of DBW (option code JL4) and that they have a regular A/C request line like the 2002 and older trucks. So then all you would have to do is flash your PCM to a van OS and it should work. I have the wiring diagrams to back this up, A/C request line and DBW, but the wiring from the TAC to pedal on the van only has 6 wires, where as the truck has 9. I have been told that shouldn't be a problem as long as the TAC and pedal match. This is where I am currently, but now the PCM tuners I have talked to say that vans DIDN'T have DBW until 2005. I haven't seen a wiring diagram for a 2005 Express van yet, so I'm not sure what they are using to control the A/C, but I am looking into it. If they didn't use the serial data, then this may be the way to go.

 

This is true, but it will momentarily bog the engine down until the PCM bumps the idle up, not horrible, but not nearly as smooth and seamless as the PCM controlled A/C.

 

I wondered if you hooked the car compressor demand signal that engages the clutch to the one non-data wire that goes from the HVAC Module to the Clutch if that wouldn'e control the compressor.

It is kind of like the car demand signal powers up the clutch but the PCM gets to decide if it wants to let it run based on head pressure in the system.

I guess I can try it and if it doesn't work, I will have to fall back to a stand alone AC system.

 

I didn't have the HVAC module, so don't know. I'll hopefully get it figured out before summer though. Still gotta finish putting engine in my 68 C20.

 

On another forum, it was recommended that I call Street and Performance and ask if they had a solution.

So I called S&P and talked to Mark.

He says that he runs the AC as a seperate system for this
configuration of motor to avoid the problem with having to have a
seperate HVAC module to signal the compressor to turn on.

He went on to say that the idle control isn't very noticiable with
the compressor turning on and off. To mask a little bit of
bogging, he recommends bumping the idle up 50 RPM over factory in
the PCM.

He also recommends the fans not be controlled by the PCM, but by a
seperate fan controller with the temp sensor at the bottom of the
radiator set to about 175F. He said with this setup, the fans will
run about 50% of the time. So basically, if there is 20F delta
temperature across the radiator, the fan stays off. (he's in
Arkansas - it might run a little more in Phoenix!)

The controller he's recommending is on page 134 of the Street and
Performance .pdf catalog.

Regards,

Phil

 

Thanks, I might try that later, with another relay to kick the fans on when the ac gets turned on.

 

To make the Fans kick on when the A/C kicks on. All you need to do is run a splice from the A/C clutch 12v+ to the 12v+ signal side of your low and high speed relays. Just make sure you put a Diode in the PCM signal wire as to not backfeed the 12v+ back into the PCM. I had it this way on my 94 S10 and it worked flawless.

 

There are 2 setups both are covered in the Holden engine control manual. The BCM conrols the setup but you may be able to figure something out with the diagrams located here:

http://www.sr510.com/tech/Holden_LS1.pdf