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Thread: P59 & a/c

  1. #1

    P59 & a/c

    Hello,

    I've read a lot of posts about getting the A/C working on the Gen 3 ECMs, but only ended up more confused. This isn't my first go at A/C, and I got everything working well on an older Gen 3 ECM (Blue/Red), but can't get my P59 ECM (Blue/Green) to trigger the A/C relay when I turn the A/C on. If I go into HP Tuners scanner and manually turn on the compressor relay, everything works as should, compressor engages, if temp is over 200* fans turn on, idle doesn?t stumble. I know that my P59 used Serial Cycling originally, but setting this to any other setting made no difference, Analog, Analog Cycling. I am trying to trigger at idle with 12v to C2 17, and ground to C2 55 and have tried both the +&-, only + and only -. The only thing that seemed to make a difference was when I switched type to Passive, I could no longer trigger the compressor relay manually. I never tried "Not Fitted". I don't have any pressure sensor(s) connected to the ECM, but have a binary switch in-line with my 12v request signal and I am getting 12v through this switch. Under the tab, System-A/C-Hardware-Recirculation Fitted, I have that set to Fan #2 but tried AC Recirc as well. Setting that to AC Recirc, I was no longer able to turn on my #2 Fan from the scanner.

    I'm at a loss as it seems others have gotten this to work, am I missing something? I'd hate to resort to a trinary switch to control fans and not have any bump in idle or RPM deactivation. This is a stand-alone setup, originally the ECM vehicle was a 2003 Yukon 6.0, only big change was I segment swapped to 4L80. OEM type compressor, 10S17F Four Seasons 78377. The only thing I can think of is, reading the post "A/C request Blue/Green connector ECU" at ls1 tech, I need to add the three-wire sensor (GM 13587668) to the high side refrigerant line. I can't see needing to add the two-wire sensor (GM 89040362) as this just adds/removes ground to the HVAC module, which I don't have. I'm monitoring in the scanner, A/C request, A/C Active, A/C Clutch Engaged, and A/C Disable (pressure). I never get A/C Request to go to yes nor get A/C Disable to go to yes, so is the 3-wire sensor still needed since it doesn't appear to be pressure stopping it from engaging? Manually turning on the compressor will get A/C Active and A/C Clutch Engaged to go to yes , but A/C Request and A/C Disable stays at no . Any help is greatly appreciated! Brendan
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    Last edited by Brendang2000; 08-02-2020 at 12:07 PM.

  2. #2
    Tuning Addict blindsquirrel's Avatar
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    You need the pressure switches/sensor for whatever 'Type:' you have it set for. It's never going to control the compressor on its own unless it sees valid info from the correct type of switch/sensor.

    Essentially, the pressure switch setup you have corresponds to Type: Not Fitted (i.e., the PCM is not expected to control clutch activation).

  3. #3
    Quote Originally Posted by blindsquirrel View Post
    You need the pressure switches/sensor for whatever 'Type:' you have it set for. It's never going to control the compressor on its own unless it sees valid info from the correct type of switch/sensor.

    Essentially, the pressure switch setup you have corresponds to Type: Not Fitted (i.e., the PCM is not expected to control clutch activation).
    Thank you for your reply! OK, I think I follow you, but still not 100%. So when mine was originally Serial Cycling, it required the serial data from the HVAC module plus the pressure signal which was originally equipped (GM 13587668). However, if I change type to Analog (Cycling) shouldn't it be triggered via 12v on C2 17 (possibly ground on C2 55 for cycling) and not require any pressure signals since Analog didn't have any pressure signals connected to the ECM, like Express Vans? If so, I am still unable to trigger the relay with type set to Analog or Analog Cycling.

  4. #4
    Tuning Addict blindsquirrel's Avatar
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    What flavor of Express van had no pressure switches?? That's not possible if the compressor is PCM-controlled. It has to have some way of knowing if the compressor needs to be on or off.

    2003 Express compressor controls diagram:

    2003 Express compressor controls.png

    Low-side switch is just sharing the clutch coil ground so don't let that confuse you. Signal from the switch goes back to C2 #55. Switch is normally open: zero PSI equals open circuit. Zero PSI means clutch commanded OFF. Right now without a low-side switch wired in the PCM is reading that as zero PSI and is not going to command the clutch ON when it thinks the A/C system is empty.

    I am basing this off the assumption you're using Express van tune settings, that means you have to use the Express van pressure switch arrangement. If not, you need to pick a system and then copy it.

  5. #5
    Tuning Addict blindsquirrel's Avatar
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    Oh, forgot. The high-side switch is drawn incorrectly in the diagram, it should be shown as normally closed. So it's not required for the clutch to engage, but it needs to be there as a safety device.

    A/C Pressure Switches

    The A/C system is protected by two A/C pressure switches.
    ? A/C low pressure switch
    ? A/C high pressure switch

    The A/C high pressure switch interrupts the A/C request signal when the A/C line pressure is more than a predetermined value. The A/C low pressure switch interrupts the A/C low pressure switch signal when the A/C line pressure is less than or more than a predetermined value. When the powertrain control module (PCM) stops receiving the required signals, the A/C compressor clutch relay control circuit is no longer grounded, disengaging the A/C compressor clutch. The A/C compressor clutch is disengaged under the following conditions:
    ? A/C low pressure switch is less than 124 kPa (18 psi).
    ? A/C low pressure switch is more than 338 kPa (49 psi).
    ? A/C high pressure switch is more than 2896 kPa (420 psi).

  6. #6
    Quote Originally Posted by blindsquirrel View Post
    Oh, forgot. The high-side switch is drawn incorrectly in the diagram, it should be shown as normally closed. So it's not required for the clutch to engage, but it needs to be there as a safety device.
    I'm using the truck tune (GMT800), I just looked at an express van ECM that I have. Sorry, I saw the pressure switches but they doesn't send a signal like the three wire sensor, so that could be tricked by applying/removing ground or +12v, correct?

  7. #7
    Tuning Addict blindsquirrel's Avatar
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    According to the diagram, yes, for testing it should read a jumper wire from C2 55 to GND the same as a valid low pressure switch.

    Now, the catch is, I don't know if anybody can guarantee that all P59s with all operating systems have all the parts inside to enable reading all possible variations of pin configurations across all the various platforms. Do you know if the '03 Express and '03 Yukon use the same Service Number? The Yukon diagram shows C2 55 as unused, of course. If they are different SNs the Yukon part may just not have the board-level components inside connected to that pin. Also the Yukon OS may not respond properly when the 'Type:' settings are changed over to match the Express van. I've seen that before on some fan controls on other ECMs. The menu of options is there in the tune but it doesn't change the operation of that assigned pin like it should.

    Looks like you can pick up a pre-programmed P59 on ebay for $65... if you were to supply them with VIN 1GCHG35U131147731, you'd get one for a 2003 Express 3500, 6.0 & 4L80E.

  8. #8
    Thanks blindsquirrel, you've been very helpful!! It seems that to get this to work, I still need to send the ECU pressure signals via the 3 wire sensor, or trick the ECU into seeing the correct voltage by jumping a 50k ohm resistor between C1 45 & C2 14 (the resistor might not be a permanent fix though), set Type to Analog (NOT cycling), and set fans to correct pressures 190 low, 240 high (got most of this from autocomman's post @ ls1tech). If I am still unable to get it to work, then I think maybe this P59 does not have the hardware to activate the compressor via C2 17.

    I can no longer see the service number on the Yukon ECU as it's installed (trapped) in the car. It may take me a while to make the hardware changes (get resistor or install sensor), but I'll reply when I do to hopefully say it worked. Again, thanks for your input blindsquirrel!!

  9. #9
    Tuning Addict blindsquirrel's Avatar
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    No, you know the internal hardware for C2 17 is present as you can manually command it on with the special functions. It's the reading-a-signal-on-C2-55 that would be the potential issue. I only checked Rock Auto for the PCM lookup, there's no listing for the Yukon PCM but several options for the Express, that leads me to believe they are different, otherwise they would be the same parts listed under both models.

    Is there a channel in the scanner for that low pressure switch status? There probably won't be since the supported channels list is based on the operating system, and the Yukon OS didn't use that.

  10. #10
    Tuning Addict blindsquirrel's Avatar
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    And I don't think faking the Yukon's sensor signals would tell you anything useful as a test. You already know the Yukon PCM with the Yukon OS & settings will work with the Yukon pressure sensor inputs.

  11. #11
    Tuning Addict blindsquirrel's Avatar
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    Finally realized a batter way to say what I was getting at in the last post. I'm slow that way sometimes.

    The Yukon is set up for Serial Cycling. The low side switch status is sent to the PCM over serial data.

    2003 Yukon compressor controls (serial cycling).png

    So say you set up a test replicating a valid pressure sensor signal at C2 14, and change the tune to Analog Cycling. What pin do you put the low side switch (or test ground) to?? The same pin we're suspecting of not being connected to anything inside the PCM?

    There's really no good way to nail down whether it's an internal hardware issue with that pin in that specific Service Number, or an issue with that specific OS not able to look at the pin to get the switch status.

  12. #12
    Quote Originally Posted by blindsquirrel View Post
    No, you know the internal hardware for C2 17 is present as you can manually command it on with the special functions. It's the reading-a-signal-on-C2-55 that would be the potential issue. I only checked Rock Auto for the PCM lookup, there's no listing for the Yukon PCM but several options for the Express, that leads me to believe they are different, otherwise they would be the same parts listed under both models.

    Is there a channel in the scanner for that low pressure switch status? There probably won't be since the supported channels list is based on the operating system, and the Yukon OS didn't use that.
    Sorry so long returning to your posts Blindsquirrel, car was at the alignment shop and couldn't get back to it until now. You are correct, there is no low pressure status in the scanner, but I can view voltage on AC Pressure Sensor, which has to be the three wire as it's looking for voltage. Are you are correct with C2 17 definitely being there as that pin is not used in the Yukon OS? I'm triggering the compressor relay in the scanner and it sends voltage down C2 43 (circuit 459).

    My thought process about the program and sending a "fake" signal, should make it look like the pressure (actually voltage) is in the correct range and therefore enable the program to kick the compressor on; although I'll need to make sure pressures in the tune match. I have both resistors and the correct pressure sensor on order, but not sure if the sensor plugs into a service port or a proprietary port, so I may be trying the resistors first as I may need to vacuum the system down and have that port installed. Be nice if it's a service port, I'll just install it and see how it works as I'd rather not use the resistors.

    For switching to Analog, it's my understanding that I can not use Cycling, it needs to be just Analog. I would be sending ground to C2 55 and the request (+12) becomes C2 17. I think after I have the pressure sensor installed, we'll know for sure if this P59 has the internal hardware to be able to accept "Analog". Again, I'm getting most of this info from autocomman (ls1tech) as he says he has gotten this to work on a 2003 2500 Silverado. So I'm hopeful. Thanks Blindsquirrel, I'll update when I make some progress.

  13. #13
    Tuning Addict blindsquirrel's Avatar
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    Sorry, you're correct, C2 17 is the request pin, C2 43 is the relay control output.

    You know, looking at the Express van diagram gives some clues. It shows a pullup resistor on pin 55, and a pulldown resistor on pin 17. You should be able to measure those pins with an ohmmeter (PCM out of vehicle) to see if those parts are on the board inside. #55 should have continuity to either the +12v or +5v pins (no way to know from just the diagram is it's 5 or 12v), and #17 should have continuity to the ground pins (all the sensor low reference and power ground pins should be tied together inside, common).

  14. #14
    Tuning Addict blindsquirrel's Avatar
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    If this is a non-variable displacement compressor, it works by cycling the clutch based on the low side pressure. I don't like the idea of trying to patch this together with only a 3-wire sensor on the high side and leaving the PCM completely blind to what's happening on the low side. You might can get it to turn the clutch on that way but it won't be right.

  15. #15
    Unfortunately with the Yukon ECM installed, I don’t think I’ll be able to reliably get to the pins to try the tests you mentioned. I’ll give it a try in the next few days anyway.

    From what I have read, the Vortec Truck engines used fixed type compressors, so I believe my 10S17F is the fixed type. I do have a binary switch in the high side in line with the A/C request signal (which will be C2 17), which according to Vintage Air, monitors both high and low pressure although done through only the high side. If pressures exceed the switches parameters, the signal would be cut going to the ECM and it will shut off the compressor; basically it’ll look like I turned off the A/C. Are you thinking it would be best to monitor the low side as well? If so, I can install a low side switch in-line with the compressor clutch’s ground, so it would cut power to the clutch if pressures are wrong, much like how the Express Van’s system works. The Yukon did this as well, but sent the signal to the HVAC module. Thanks for all the input blindsquirrel!!

  16. #16
    Tuning Addict blindsquirrel's Avatar
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    No. A binary switch, if it's located on the high side, can only function as a low-refrigerant safety. It cannot cycle the clutch in normal operation.

    This is still just a plain 'ol CCOT system. Cycling Clutch, Orifice Tube. The PCM is only tied in so that it can do value-added shit, like adjust idle speed based on compressor state, disable the compressor under conditions like engine overheat or WOT.

    The Yukon, using Serial Cycling, with its 3-wire high side sensor, still requires a low side cycling switch. It just happens to go to the HVAC panel and send its status to the PCM over serial data, rather than being wired direct to a PCM pin. It still uses the low side switch as a cycling switch. You can't delete the cycling switch from a CCOT system and expect it to control itself with magic.

  17. #17
    Quote Originally Posted by blindsquirrel View Post
    No. A binary switch, if it's located on the high side, can only function as a low-refrigerant safety. It cannot cycle the clutch in normal operation.

    This is still just a plain 'ol CCOT system. Cycling Clutch, Orifice Tube. The PCM is only tied in so that it can do value-added shit, like adjust idle speed based on compressor state, disable the compressor under conditions like engine overheat or WOT.

    The Yukon, using Serial Cycling, with its 3-wire high side sensor, still requires a low side cycling switch. It just happens to go to the HVAC panel and send its status to the PCM over serial data, rather than being wired direct to a PCM pin. It still uses the low side switch as a cycling switch. You can't delete the cycling switch from a CCOT system and expect it to control itself with magic.
    Sorry, I think you are incorrect on the type of system this is as it’s a TXV system, expansion valve; vehicle is an AMC Rambler with an aftermarket under-dash evaporator. I do see your point with the PCM really only controlling value added stuff and that since my compressor is of the fixed type, it should still have the low-side switch to facilitate cycling which my high-side switch will not do (protection only).

    The 3-wire sensor arrived and I currently have no way to install it, so the system will need to be evacuated so I can get everything installed. While the system is open, I’ll install the 3-wire sensor, a low side switch for cycling and I’m going to swap that binary for a trinary as a "just in case". If I can’t get the PCM to work, I’ll at least be able to kick my fans on via the trinary without having to vacuum the system down again. All this is going to take me a while, but will report back when I finally get this all installed and tested. Thanks for the input and knowledge blindsquirrel, it’s very appreciated!!

  18. #18
    Tuning Addict blindsquirrel's Avatar
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    Well. A TXV does not cycle the clutch to regulate the low side pressure, it does it directly. The CCOT systems have to infer the evaporator temp by means of the low side pressure - low pressure equals low evap temp, and the compressor disengages to prevent freezing up. The TXV reads the evap temp directly and increases or decreases the flow accordingly, clutch stays engaged, does not cycle, most do not even use a low side switch as a low refrigerant safety, they just keep on truckin'.

    To be honest I don't have a clue where to start on how to convert a CCOT compressor and PCM to work with TXV plumbing.

  19. #19
    Well I guess my wiring chores just got easier then I'm still going to install the hardware I mentioned, but skip wiring in the low-side switch and see how far I get. I am running this setup as a "dumb" system, no PCM integration, in another vehicle, so I know I can at least get the system to work without the value added stuff. It's been near or over 110* here since July 26 and the forecast isn't getting any better, so A/C is a must! lol

  20. #20
    Ok, got an update finally. Got the pressure sensor (3 wire) installed and verified it was reading in the PCM, but still no go with either Analog or Analog Cycling. So next I tried connecting the van PCM up (it's just laying across the fender for now) and changed most parameters to match the Yukon's PCM, but left the type as GMT610 and 4.8ltr (but increased the Cylinder Volume). I left the A/C type to Analog Cycling and it still would not turn on; I was starting to doubt my wiring. I'm logging A/C Request in the scanner, but it never changed to YES. Next I tried changing A/C type to Analog, and now it works! Fans come on too, but seem to stay on after turning off the A/C, have to see what's going on here, maybe temp related. So I'm thinking that not all P59s have the required hardware to run Analog A/C. When I finally get the Yukon PCM swapped (it's really hard to remove), I'll check and see if I get continuity on the pins for the Analog circuit. Hopefully I'm not going backwards with changing this DBC PCM to DBW, I did enable ETC in System Options.