3.1EyeCandy

iTrader: (3)

n the spirit of making (or potentially making) somewhat questionable decisions, I've been thinking of how to best wire an Air Conditioning compressor in a thirdgen. There are many posts on this, here, on ls1tech, and other places on the internet. They effectively give 3 options:

1. Use the 4th Gen variable displacement A/C compressor along with the 411 PCM, a Camaro OS, and the requisite 1999-2002 A/C wiring including the pressure sensor. AKA - copy the 4th gen fully
2. Use a fixed displacement A/C compressor (R4 or Sanden) and run it completely independent of the PCM.
3. Use option 2, but run a signal wire from the A/C compressor to the PCM to inform it that the A/C compressor is enabled, which will adjust the idle.

There are actually more options if you get into using a non-Camaro OS with the 411 PCM (like an Express Van), which can use high and low pressure switches - but this will then have some additional difficulty running dual electric fans. Often when searching for achieving PCM control of a fixed displacement compressor (R4 or Sanden), I'll run across that PCM control will only work with a variable displacement compressor and that the A/C pressure sensor is intended for specifically that scenario. Then people go back to recommending mainly options 2 or 3 above, or entertaining the Express van OS and its use of pressure switches instead of a sensor.

But what if this is actually much simpler? Can we use a fixed displacement A/C compressor (like an R4 or Sanden), run the Camaro OS on the 411 PCM to get dual electric fan control, AND get all the nice PCM control of the compressor (which allows for idle adjustment, high RPM cutoff, high pressure fan enablement, and high throttle position cutoff)? I've been reading way too many internet threads and was beginning to think through some combination of relays to emulate what the 4th gen A/C pressure sensor does to the PCM when it dawned on me...

I think this will just work. Here's how:

• Place a LOW pressure cycling switch between A/C request and the PCM. This will enable cycling of the fixed displacement compressor. The PCM does not control cycling, the switch does. It will effectively see the user turning on and off the A/C request, and enable the A/C according to the pressures it sees from the A/C pressure sensor and other sensors (RPM, TPS).
• Place the A/C pressure sensor in the high side line. This enables:
  • High pressure cutoff (which the Sanden compressor lacks, and won't hurt on an R4)
  • Enablement of fans at different pressures
  • High RPM and High TPS disablement of A/C compressor
• The low pressure cutoff behavior of using the pressure sensor has been described by some as a potential issue, as at 30 PSI it is higher than where the R4 or Sanden operates normally (seeing online pressures in the 20s). I don't believe this is an issue, however, as the sensor is in the HIGH side line. That side should NEVER see pressures lower than 30 unless there is a freon leak. Low side pressures are not being measured, and will operate according to the pressure cycling switch from the thirdgen.

Here's the diagram I made out. It's nearly identical to the 1999-2002 Camaro LS1 diagram, with the addition of a pressure cycling switch in the low side between then A/C request and the PCM. I've tried to also document out PCM function underneath the diagram to help myself (and others potentially) think through expected operation. I've read through the online factory manual pages I can find and thought through how the PCM should respond given the readings of the pressure sensor and included those notes. I'm thinking this should work, but I also haven't found this well explained or as "the way you ought to do it" anywhere, so really questioning if I'm missing something. Please note that I can also be a bit dense when reading others' posts on what to do and why, particularly when the language isn't clear or glosses over a detail - so I may have overlooked somebody recommending exactly this. Sorry.

If you've got experience with the 411 PCM and A/C, I'd love some feedback. I want to know if this will work, and if not - WHY. My goal is to put the wires I need into my harness and PCM connectors and not have to remove them, so figuring this out is important to me.




Changes since original posted diagram:

• Recreated PCM diagram in draw.io (program I'm using for schematics) instead of using an image. Seems to produce a little cleaner image which diagram is exported.
• Added explanation of "LOCAL Connector" planned to be used on my car
• Added note about usage of a A/C High Pressure Cut-Out Switch, if required by the compressor
• Adjusted all wire sizes - 18 AWG for all sensors and switches (for tensile strength based on online recommendations) and 16AWG for any wire leading to compressor clutch (to handle expected amperage).
• Added note about A/C diode function

86White_T/A305

Following this as Id like to eventually add ac to my next project with a 411pcm..and maybe cruise control with a manual. Lots to figure out.

ULTM8Z

Not sure if this helps, but I recently helped a friend with a LS swapped 91.

Below is the schematic I ended up with that got his system to work.

86White_T/A305

That is helpful, now I also have to figure out what exact high side and low side switches I need to order for the system to work. There seems to be quite a few variations listed on rockauto. Not having any of the original system intact makes this a guessing game of what I should use.

QwkTrip

iTrader: (22)

This whole thing confuses me too. According to Rock Auto, the service replacement for 2000 Camaro 5.7L is a "V7" type compressor.

And according to this Delphi website, the V7 is a variable displacement compressor that "Improves air conditioning performance and fuel economy because of its smooth, continuous operation without clutch cycling."

But when you look at the 2000 Camaro wiring diagrams, it is obvious that the 2 pin connector at the compressor is just an old school clutch switch, not a variable displacement pressure valve with "continuous operation without clutch cycling".

So is the Camaro AC compressor just an over glorified compressor that's actually being used like an old school fixed displacement pump? If so, then it should be compatible with the old school controls in the 3rd gen too, right?

ULTM8Z

For what its worth, I adapted a Sanden FLX7 compressor to my serpentine system. Granted I have a Classic Auto Air system, but I used to have a R4.

The FLX7 compressor really woke the system up... it'll freeze you out of the car even on a 90F day.

I'm not sure what performance improvement the variable compressor would yield at that point.

I also have the ECM programmed to turn the compressor off at 25% TPS. During typical driving, the car has so much power I'm never above 25% for more than a few seconds if I want some more than normal acceleration. Otherwise around town or cruising on the freeway I'm typically never above 15% TPS. So the compressor turning off momentarily doesn't result in any noticeable drop in vent output temperatures.

3.1EyeCandy

iTrader: (3)

@ULTM8Z thanks for sharing your diagram. Are you saying you used that schematic with a fixed displacement compressor (R4 or Sanden) OR a 4th gen compressor? Is the diagram complete? I see pin blue 45, which is the 5V reference signal for the pressure sensor, isn't hooked up. Also missing a diode near the compressor.

In your second post you mention the FLX7, which is what I'm going to try and use as well (if I remember correctly). I'm assuming you're running that on the car in your signature though with factory type wiring (low pressure cycling switch, high pressure cut-off switch, etc.). Just checking.

3.1EyeCandy

iTrader: (3)

@QwkTrip I would think that the connector on the 4th gen A/C is identical in function to the 3rdgen connector - 1 pin to supply voltage and another to use for grounding the compressor, with a diode tied between the two pins to prevent voltage surge when the compressor invariably stops (like when disabled by the user from within the car). Technically, it also makes sense that someone COULD use the variable displacement compressor with 3rd gen controls and wiring if they dropped the low side pressure cycling switch from their thirdgen wiring (note they would be missing a high pressure cut-off switch in this setup, but apparently many cars never had them and they seem to be there more for environmental than safety reasons), although I'm not sure why they'd want to. From everything on thirdgen people have written, the general consensus is that achieving the same level of cooling with the 4th gen compressor takes upgrading other components of the system to match what the 4th gen used, which few people do.

I found this answer on Stack Exchange helpful in understanding a variable displacement compressor with internal control: https://mechanics.stackexchange.com/...sor-controlled.

ULTM8Z

This LS swap car I worked on was a few years ago, so I don't recall all the details. But I believe it was a Sanden style compressor. Also if I recall correctly, I believe he opted to omit that sensor as there was no where to put it. We did put a diode on the compressor, even though it's not indicated in the diagram.

I used the FLX7 on my 2nd gen. Though I believe the CAA system only uses a high pressure cutoff switch.

dixiebandit69

I still don't have the AC functioning on my swap yet, but when I do, I'm going to do it as mentioned in this thread.

dabomb6608

iTrader: (3)

Would it be worthwhile to upgrade to a single brushless fan (like C7 Vette fans) that way you could then run the Van OS?

I am not LS but I plan on converting my Mark VIII fan to a brushless fan & shroud setup when I do my AC install. My EBL Flash has parameters that allow me to shut down the AC above certain RPMs or when in PE mode. As well as a engine start delay.

I've heard those fans move a crazy amount of air and are significantly less power hungry then say the Taurus/Mark VIII fans. Can be setup to be variable speed fans too that only kick into high speeds when needed (or when AC on).

QwkTrip

iTrader: (22)

That is extremely helpful, thank you!

Chuck!

https://www.thirdgen.org/forums/ltx-...reen-blue.html

This is how I got it to work with a 243 pcm and 04 CTSv compressor with a trigger&ground switch on the compressor. I think it'd be pretty close for a 411.

QwkTrip

iTrader: (22)

That's exactly what I needed to know, thanks!

3.1EyeCandy

iTrader: (3)

@dixiebandit69 Thankyou!

This is actually one of the many posts I read in getting to my diagram. I found the post from branndonw informative (as well as your replies), but a little confusing at the time given I'm using the red/blue 411 PCM (a P01 controller) and not the newer blue/green PCM (a P59 controller) and wasn't sure at the time that the connected pins on the PCM would be the same. I also didn't immediately follow your back and forth (one of the disadvantages of reading on a phone or late at night).

However, I now believe his pin references are correct for both controller types after reviewing it again. His wiring diagram (the combination of yours, his, and a modification to the pin-out) is functionally identical to what I've posted here with the exception of omitting the high pressure cut-off switch as the pressure sensor will be performing that role in my diagram (and the Sanden I hopefully will use does not have a high pressure cutoff switch location to use). If a compressor was being used with such a provision (like the R4) - there is no harm in routing the A/C request signal through the high pressure switch, the low pressure cycling switch, then to C2 17.

Really glad you pointed this post back out as it effectively confirms that what I've proposed has been in use by someone and working well. I'll spend some time cleaning up my diagram and adding an optional routing through a high pressure switch (not required given the sensor, but won't hurt anything) for those with an R4 compressor or other with such a switch. (Edit on 7/26 - updated diagram).