AC wiring with ECM control clutch/fans
10-11-2016, 04:08 PM
#1
AC wiring with ECM control clutch/fans So I'm trying to figure out how to wire my AC . I been looking in different forums and it just seems like the information is scattered and not well organized. Would love to have a how to on a few different scenarios. My swap is a 2005 5.3 going to a 1989 S10 Blazer . I'm using a Sanden Compressor. How to I get the ECM to control my AC compressors and fans. What parts do you need etc. would love for this to be a sticky. Thank you in advance and I'm sorry if maybe this information is out there and I didn't find it.
Here are a few pictures , that plug with 2 wires was plugged into my old compressor, but my Sandem compressor has one wired HMMMMMMM.
Here are a few pictures , that plug with 2 wires was plugged into my old compressor, but my Sandem compressor has one wired HMMMMMMM.
Last edited by Ogoz23; 11-03-2016 at 12:01 AM.
10-12-2016, 03:53 PM
#2
Refer to a 99-02 Fbody LS1 for simple computer controlled AC. Emulate that with the trinary pressure sensor and clutch relay
Fans can also be based off 99-02 V8 cars or run both fans independently. Stock, 3 relays are used to turn single speed fans into dual speed and both run together. If ran individually, one comes on then both come on for high function
You may have to switch to an older PCM because some truck PCMs cannot control electric fans or an AC relay (missing hardware)
GM AC compressors have two wires, 12v to the clutch and clutch ground
Aftermarket only have the 12v. Ground is either a short lead grounded directly to the case or grounded internally
To use with a common swap harness, cut the supplied connector off and splice onto the wire that isnt black. The correct color is dark green, but mfrs often choose their own color scheme, so it can vary
Fans can also be based off 99-02 V8 cars or run both fans independently. Stock, 3 relays are used to turn single speed fans into dual speed and both run together. If ran individually, one comes on then both come on for high function
You may have to switch to an older PCM because some truck PCMs cannot control electric fans or an AC relay (missing hardware)
GM AC compressors have two wires, 12v to the clutch and clutch ground
Aftermarket only have the 12v. Ground is either a short lead grounded directly to the case or grounded internally
To use with a common swap harness, cut the supplied connector off and splice onto the wire that isnt black. The correct color is dark green, but mfrs often choose their own color scheme, so it can vary
10-12-2016, 08:51 PM
#3
Oh man if I need another pcm this is getting to complicated . I'm converting from DBW to DBC and for it to work I had to get a pcm that supports DBC. Now if I have to get another pcm for the AC it's going to be a mission because in order to trouble shoot I have to buy the harness and get the pcm flashed To start the motor to delete the vats ...
10-13-2016, 11:27 AM
#4
If you're switching PCMs for the TB, then go with a common 0411 box. It controls everything you want and is super common. Remember to compare pinouts from the 05 PCM to the 99-02, a few wires moved. After that, shave the locator tabs on the green PCM covers and it will work
Add the necessary pins for Fans and AC along with any other additions you may want
Add the necessary pins for Fans and AC along with any other additions you may want
10-13-2016, 07:09 PM
#5
Correct me if I'm wrong. When I turn on my AC from the HVAC Controls, a signal is sent from the cab via 2 wires. one wire gives powers the blower and the other goes to the low pressure cut off switch which turns on the compressor. I have to tap into from one of those 2 wires to connect to the ECM . So I'll be sending a signal to the ECM that the AC is on. I don't understand how the ECM controls the AC if there is only one AC wire from the ECM and that wired just receives a signal .. unless there is multiple AC wires going to the ECM one to receive a signal and one to sent a signal ...
Last edited by Ogoz23; 10-13-2016 at 07:18 PM.
10-16-2016, 06:40 AM
#6
The 12v signal from the HVAC headunit is considered "AC Request"
With the 99-02 method, the PCM receives a request signal and enables, the relay, reads the sensor and gets feedback when the compressor clutch is engaged so it can bump idle
All of the other functions are not related to the headunit, so they do not come or go from it. They are PCM controlled instead
With the 99-02 method, the PCM receives a request signal and enables, the relay, reads the sensor and gets feedback when the compressor clutch is engaged so it can bump idle
All of the other functions are not related to the headunit, so they do not come or go from it. They are PCM controlled instead
10-16-2016, 10:42 AM
#7
Thank you ! Since I already have a 2007 pcm from and express van , how would the wiring work . Does it make things that much complicated that I'm better of buying a 0411 pcm ?
You put that the pcm reads the sensor . What sensor is it reading ?
You put that the pcm reads the sensor . What sensor is it reading ?
Last edited by Ogoz23; 10-16-2016 at 10:52 AM.
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10-17-2016, 05:30 PM
#10
Heres a few diagram:
LS1 Fbody. Full PCM control with a 3 wire trinary pressure sensor. Really cant get much simpler for full PCM control
http://lt1swap.com/pictures/18_ac_comp_controls.gif
Heres how early trucks do it, pretty confusing and mismatched so i dont go by this alot. The high pressure switch is in the backside of the compressor much like old R4 units
http://lt1swap.com/pictures/99_02_sc...00%20truck.gif
Heres a simpler method to do the same. Substitute the compressor clutch pin on whatever LS PCM you're running and it fit the bill. Simple via two switches and a feedback wire
http://www.austinthirdgen.org/mkport...F_and_vin8.jpg
Make sense?
LS1 Fbody. Full PCM control with a 3 wire trinary pressure sensor. Really cant get much simpler for full PCM control
http://lt1swap.com/pictures/18_ac_comp_controls.gif
Heres how early trucks do it, pretty confusing and mismatched so i dont go by this alot. The high pressure switch is in the backside of the compressor much like old R4 units
http://lt1swap.com/pictures/99_02_sc...00%20truck.gif
Heres a simpler method to do the same. Substitute the compressor clutch pin on whatever LS PCM you're running and it fit the bill. Simple via two switches and a feedback wire
http://www.austinthirdgen.org/mkport...F_and_vin8.jpg
Make sense?
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trobert3 (05-29-2021)
10-17-2016, 06:56 PM
#11
First link: in this method I see that my signal from my HVAC controls go straight to the PCM. I also see that a pressure sensor is sending 2 signals to the PCM. in this method I see the ac clutch is being trigger by the PCM via a relay .
Last link looks like its the simples . from what I see in the diagram my signal from my HVAC controls go to a pressure cycling switch now that switch is connected to a high pressure switch and from the high pressure switch that signal goes to the ac clutch and the pcm . now the pcm knows that the ac is on and turns on the fans?
so do I got it ?
I also see a clutch diode do I need this ?
Last link looks like its the simples . from what I see in the diagram my signal from my HVAC controls go to a pressure cycling switch now that switch is connected to a high pressure switch and from the high pressure switch that signal goes to the ac clutch and the pcm . now the pcm knows that the ac is on and turns on the fans?
so do I got it ?
I also see a clutch diode do I need this ?
10-17-2016, 08:54 PM
#13
TECH Apprentice
Thanks Pocket.
Ogoz23 Hope you don't mind me jumping in.
I see where the van ECM (X1 pin 63) supplies the 12VDC ground for A/C Compressor Clutch control relay. How does the ECM know you want the AC on?
I guess what I'm asking is how do we tell the ECM we want AC and should we let the ECM control the clutch relay. Will this in turn control the electric radiator fans as well as bump the idle up.
Ogoz23 Hope you don't mind me jumping in.
I see where the van ECM (X1 pin 63) supplies the 12VDC ground for A/C Compressor Clutch control relay. How does the ECM know you want the AC on?
I guess what I'm asking is how do we tell the ECM we want AC and should we let the ECM control the clutch relay. Will this in turn control the electric radiator fans as well as bump the idle up.
10-17-2016, 09:05 PM
#14
I'm still learning and pocket has been a great help , but I believe the ECM has an input for the pressure sensors and an input for the ac request that tells the pcm the ac is on and to start reading the pressure sensors and decide when to turn in the clutch on ..
10-17-2016, 09:38 PM
#16
TECH Apprentice
Yes Pin 34 is a 5VDC reference voltage out to GM's pressure switch (same as the VA Trinary? unlikely) then it has a low (pin 13) and high (pin 12) return to the ECM. I still don't see an AC request input to the ECM.
10-17-2016, 09:47 PM
#17
Maybe it uses the signal of the switch as an AC request ? I wonder why the pcm has to provide 5v to the pressure switch or the pressure switch is providing 5v to the pcm .. is that all it takes to trigger the clutch ? The more I read up on this it just seems like their is so many types of pcm setups that I don't know the correct answer ..
10-17-2016, 09:53 PM
#19
This thread is going to get real messy if you start throwing different years in the mix. Starting in 2008, the vans went to a serial data A/C request rather than the 2007 and earlier 12v A/C request. On an '08, the request is through the low pressure switch, then sent to the BCM, the BCM then sends the request on a serial data line to the PCM, and it is what controls the A/C clutch relay based on the pressure sensor which is a three wire sensor.
The older van A/C request the 12v goes from the A/C controls on the dash to the high pressure cut out switch and then to the PCM. The low pressure switch also is hooked to the PCM and grounded on the other side, so the PCM can tell whether or not the switch is open or closed and makes changes based on that, and if the parameters are met, it sends a signal on yet another wire coming out of the PCM to the A/C clutch relay.
The older van A/C request the 12v goes from the A/C controls on the dash to the high pressure cut out switch and then to the PCM. The low pressure switch also is hooked to the PCM and grounded on the other side, so the PCM can tell whether or not the switch is open or closed and makes changes based on that, and if the parameters are met, it sends a signal on yet another wire coming out of the PCM to the A/C clutch relay.
10-17-2016, 09:58 PM
#20
The compressor clutch is an electromagnet. When the clutch is released, the magnet can recycle the current at a diminishing rate to "flutter". This is terrible for belts and the compressor, so a diode is used to prevent feedback back through the magnet
If you look at factory AC citcuits, there is either a small cream colored plastic box inline on the wire or what looks like a resin filled shrink tube a short distance from the AC clutch. The diode is in there. Older systems used a traditional diode between the terminals directly on the compressor clutch. If the OEM diode was removed, this is a simple way to put it back
If you look at factory AC citcuits, there is either a small cream colored plastic box inline on the wire or what looks like a resin filled shrink tube a short distance from the AC clutch. The diode is in there. Older systems used a traditional diode between the terminals directly on the compressor clutch. If the OEM diode was removed, this is a simple way to put it back