So I am doing a 03 6.0 swap in that 87 silvy. I am finally down to the wiring. I am keeping the 03 pcm and DBW setup. but when i look at the wiring diagrams for the 03, it says the AC request siginal is serial data. is there any way around this? id rather have the PCM knowing when the AC is on so it will kick up the idle and control the AC clutch.

If you find one, let me know. I've got an HVAC control module jammed up under my dash to get around this. Nasty hack.

That was my idea, but i was hoping there was a module that could transmit serial siginals. I was looking at a few different things, but it looks like they all need a pc to communicate. if we could just read the data its outputting and transmit that same siginal then we would be all good. isn't yours CAN based vs the J1850vpw? we have some tools at work to sniff the can buss. its made by intrepidcs.com called the neoVIfire. I want to try and borrow it to see if it can sniff J1850 buss. but then what could send those messages?

My plan was to build a module to do this. I bought a Motorola S12 based microcontroller eval board that has a CAN transciever and PHY onboard. The idea was to write a quick program to sniff the AC enable message, then send that based on an I/O pin tied to the AC enable button on the old controller.

I haven't had time to work on this, and I doubt I ever will. Hoping someone comes out with a more ready-made kit/module for CAN projects like this.

Hoo boy I think your job is cut out for you on this.

http://en.wikipedia.org/wiki/Controller_Area_Network

I think your best bet might be to use the 2003 controller. It'll take some extra work like fitting the HVAC box with the appropriate servos, but trying to add a CAN interface looks like you'll need access to the CAN network data in order to set up the messaging address which I just don't see GM releasing. The reason is you would either have to know exactly what GM's address for the HVAC system is, or be able to add a new address to the system. Trying to get someone like EFI Live to develop this capability might be an alternative. I don't even know if a dealer would have this capability even if you were lucky and found one willing to cater to gearheads.

The only other way I see to do this would be to add a separate AC button somewhere on the dash, and connect it to the 2003 controller by tearing the control module apart and extending the wires from the existing AC button to the dash button. Going this route would mean that the AC compressor would only work when the button was pushed, which to me is preferable anyway.

Speeder wrote:

The only other way I see to do this would be to add a separate AC button somewhere on the dash, and connect it to the 2003 controller by tearing the control module apart and extending the wires from the existing AC button to the dash button. Going this route would mean that the AC compressor would only work when the button was pushed, which to me is preferable anyway.

This is (close to) the way I have mine set up now. The 2007 AC module tucked under the dash is powered by the AC enable line from the 1995 module in the dash.

Speeder wrote:

Hoo boy I think your job is cut out for you on this.

It'll take some extra work like fitting the HVAC box with the appropriate servos, but trying to add a CAN interface looks like you'll need access to the CAN network data in order to set up the messaging address which I just don't see GM releasing. The reason is you would either have to know exactly what GM's address for the HVAC system is, or be able to add a new address to the system.

With a little effort I can get access to GM can data, but my setup is J1850. Also i have access to a neoVIfire. that will allow you to sniff the can bus system, and also alter can messages via a laptop. but then again im not running the can system

Speeder wrote:

The only other way I see to do this would be to add a separate AC button somewhere on the dash, and connect it to the 2003 controller by tearing the control module apart and extending the wires from the existing AC button to the dash button. Going this route would mean that the AC compressor would only work when the button was pushed, which to me is preferable anyway.

This is the way I am going to wire it for now, but when I get more time I would like to make a small interface module that would allow this to work rather than hacking up a factory module, that way I could tie it in to the factory 87 HVAC control. problem with doing that with the 03 HVAC control is the 87 is on/off and the 03 is momentary push button.

s10mods wrote:

This is the way I am going to wire it for now, but when I get more time I would like to make a small interface module that would allow this to work rather than hacking up a factory module, that way I could tie it in to the factory 87 HVAC control. problem with doing that with the 03 HVAC control is the 87 is on/off and the 03 is momentary push button.

This is why I suggested modding the heater box with the servos from a 2003 truck. The 2003 control panel will more or less fit in the same hole as the 1987 panel. This would let everything work as it would in the 2003 truck. You might even be able to use the 2003 box, but that would likely take some work.

A momentary ground should work. Put a tow - haul switch on an f-body to use the performaance
trans tables I enabled pin 58 c1 blue. Look at the truck trans schemematic tow- haul says serial data
at the pcm and bcm its happy with a grd

Speeder wrote:

s10mods wrote:

This is the way I am going to wire it for now, but when I get more time I would like to make a small interface module that would allow this to work rather than hacking up a factory module, that way I could tie it in to the factory 87 HVAC control. problem with doing that with the 03 HVAC control is the 87 is on/off and the 03 is momentary push button.

This is why I suggested modding the heater box with the servos from a 2003 truck. The 2003 control panel will more or less fit in the same hole as the 1987 panel. This would let everything work as it would in the 2003 truck. You might even be able to use the 2003 box, but that would likely take some work.

I may have done that if it was my own truck, but its not mine and I already have enough time wrapped up in this thing. I ended up putting the 03 hvac module under the dash and hooking up a remote momentary illumnated button. the 03 hvac module needs battery and ignition so I hooked the ignition to the factory 87 AC request so the only time he should ever need the button is maybe if he un hooks the battery. otherwise the 03 hvac module remembers the last function.