A/C request signal

[burtoncr]

I've been using EFILive with great success on my 93 RX7 + 06 GTO LS2 swap, but its getting a little toasty here in Texas and I want to get the AC up and running.

I've hit a snag though. The GTO "AC Request" signal routes from the HVAC controls to the BCM. Unfortunately I don't have or use the GTO BCM. All of the other AC related signals go directly to the ECM (Compressor clutch control, AC Refrigerant pressure).

So, the question, is there a way to give the ECM an "AC Request" signal, or is it a variable in a data message transferred from the BCM to the ECM?



thanks,
Chris

[ssvolvo]

Well for sure the A/C request signal is serial data and seems impossible for you to "request" it. Here's what I did. I used the A/C request from my Volvo A/C switch (12volts) to turn on the A/c relay. Forget about the actual E40 pinout. It works perfectly and the ECM (e40) will recognize the A/C through the high side (GM) pressure sensor (as long as you have it installed). The fans will work absolutely flawless as will the elevated idle. Don't ask me why I'm a mechanic not an electrical engineer!


As for your problem you could just hook the violet or yellow/black wire to your A/C relay and have it come on. Here's the schematic below.


Not to hijack your thread Chris but I hope one of the aftermarket companies will soon come out with a "programable" BCM that will work with a GM Ecm. Wouldn't it be neat to have the doorlocks and anti-theft, A/C and battery light... all that stuff work with the E40? I had to buy a tach adapter from Dakota Digital to get my factory tach to read the E40 speed signal. I guess none of the tachs use coil primary for tach input anymore. OUCH ...can you say 40 volt spike to the instrument cluster?

Probably not far down the road one might not be able to swap in a late model engine in an older rig because of all this CAN bulls#it.


I bet that RX7 is a blast to drive. My wonderful wife has a first year Z3 Bimmer with 28,000 miles she doesn't drive anymore (not even to the golf course WTF?). I am threatening to install some real LS power in that! 01 Vette motor sitting on the floor I picked up for $300 bucks. Too many project not enough time.


Good luck Chris you WILL figure it out, we all have to put our heads together:gossip: John

[burtoncr]

Well for sure the A/C request signal is serial data and seems impossible for you to "request" it. Here's what I did. I used the A/C request from my Volvo A/C switch (12volts) to turn on the A/c relay. Forget about the actual E40 pinout. It works perfectly and the ECM (e40) will recognize the A/C through the high side (GM) pressure sensor (as long as you have it installed). The fans will work absolutely flawless as will the elevated idle. Don't ask me why I'm a mechanic not an electrical engineer!


As for your problem you could just hook the violet or yellow/black wire to your A/C relay and have it come on. Here's the schematic below.


Not to hijack your thread Chris but I hope one of the aftermarket companies will soon come out with a "programable" BCM that will work with a GM Ecm. Wouldn't it be neat to have the doorlocks and anti-theft, A/C and battery light... all that stuff work with the E40? I had to buy a tach adapter from Dakota Digital to get my factory tach to read the E40 speed signal. I guess none of the tachs use coil primary for tach input anymore. OUCH ...can you say 40 volt spike to the instrument cluster?

Probably not far down the road one might not be able to swap in a late model engine in an older rig because of all this CAN bulls#it.


I bet that RX7 is a blast to drive. My wonderful wife has a first year Z3 Bimmer with 28,000 miles she doesn't drive anymore (not even to the golf course WTF?). I am threatening to install some real LS power in that! 01 Vette motor sitting on the floor I picked up for $300 bucks. Too many project not enough time.


Good luck Chris you WILL figure it out, we all have to put our heads together:gossip: John

What you said is has been my backup plan with a little addition. Maybe you arent saying this (or I can't read), but how does your compressor know when to stop? IE when the pressure is too high?

Most RX7 swappers initially used the stock Mazda on/off A/C pressure sensor in series with the A/C request to the A/C relay. That takes care of the over pressure situation, but then you have he over revving problem to deal with. I have seen more than enough exploded/broken compressors from guys who have used this method and then down-shifted or redlined with the A/C on. Thats why I want the full control from the PCM. It uses multiple variables to determine if it's "OK" to turn on the compressor, IE TPS, RPM, and A/C Request.

If what you are saying is true about the PCM recognizing pressure in the A/C lines and turning on the fan, I wonder if the PCM still controls the A/C clutch relay without the A/C Request. Maybe then the PCM A/C Clutch Control output can be tied to one pole of the A/C Relay and the 12v "A/C Request" from the dash to the other side. Thats assuming the PCM grounds the signal to turn on A/C Clutch.

[ssvolvo]

Sorry Chris,

Look at your Mazda wiring diagram I posted for you. Lower left side of the picture is the refridgerant pressure switch. This switch must be utilized between your compressor relay and compressor clutch. It shuts off the compressor at 22 psi so your evaporator won't freeze up. It will cycle the A/C perfectly. It WON'T however shut off the pump if the pressure gets too high. That is done by the thermo-switch (in the center of the diagram). It must be in your old Mazda A/C stuff under the hood. Also if things go really haywire the GM A/C pump has a relief valve installed that will blow off excess pressure.

I would make sure your fan works well when the A/c comes on. And remember if your Mazda had R-12 then add 80% of that charge in R-134.

I do lots of A/c work. If you think there's an over pressure problem you can check with guages. Really don't want much more than 300 psi on the high side.


Keep thinking man, you'll get it. John

[burtoncr]

Whats your take on disabling the compressor at higher engine RPMs?

[burtoncr]

Nevermind, found something that will work
http://mysite.verizon.net/vze7erz1/id1.html
A nice latching RPM Window Switch that I can specify the trigger points and the hysteresis.