A/C tuning

[ZJM861]

hi, the vehicle is a 87 silverado with a 2002 5.3 motor 4l60e trans.
my delima is the a/c request isnt doing chit. ive looked at the schematics and have wired it up correctly, or so i think. what settings in hp tuners would i adjust for the additional load of the compressor. under engine, idle, target idle speed, the values are the same reguardless of a/c on or off.
i have the harness set up like painless wiring and apply 12v to the a/c request and i get bubkiss. i go into vcm controls and turn a/c clutch on manualy and yields nothing either. anyone have experience in this category? im getting frustrated here.. let me know if you have any insite. thanks
clint

[Nitrous]

Are you getting voltage on the request wire at the PCM? Have you verified the high pressure switch at the condensor is working? I wouldn't mess with any HPTuner settings until you get the A/C working. No matter what the clutch should engage unless you have a wiring or relay issue. I've helped quite a few people out on their conversions and it almost always goes back to wiring, a switch or a relay.

[ZJM861]

here are some schematics and heres what ive done:
from the schematic, you dont use the high side recirc. switch being normally open.
i see that the low side switch on C2 pin 11 is normally closed, and needs ground. i currently have that wire from pcm going to ground chassis ground.

C2 pin 17 A/C request, accoring to painless says to tap that wire into the clutch 12v side, pin b. which means 12v. ive applied 12 v from the clutch side and the car doesnt idle any higher at all, still bogs down, and still dies. like i said, ive bumped the a/c on idle to 800, which is a noticable difference than 650. with hp tuners, i can turn on the clutch coil in vcm controls and no difference in idle.

C2 pin 43, the (pcm output) ground side of the clutch coil i get 14Kohmns when the (vcm controled) a/c clutch is off and 14ohmns when on. i've checked out a 2nd car, with a painless harness and his computer has the same ohmn reading. in painless' harness the C2 11 low pressure signal is grounded to the chassis.
the ohmn reading were taken from that pin 43 to battery ground.
painless' harness also doesnt use a clutch relay, they assume that your using factory a/c wiring, and thats what im doing. ULTIMATE goal is to wire it through the relay so at WOT the a/c will cut off automatically, as it should.

as far as the request wire... i dunno, im still waiting for a friend to bring his 01 silverado to work so i can remove his high pressure switch (behind the compressor) and backprobe the wire and see what voltage it has.

from what ive been told by my electronics teacher is that from the schematic on the a/c controls (hvac) the signal should be ground. ive also tried ground, no idle difference.
any of that help, hopefully i didnt confuse you with that
thanks for the insite so far, hopefully we can come to a successfull conclusion!

[Nitrous]

here are some schematics and heres what ive done:
from the schematic, you dont use the high side recirc. switch being normally open.
i see that the low side switch on C2 pin 11 is normally closed, and needs ground. i currently have that wire from pcm going to ground chassis ground.

C2 pin 17 A/C request, accoring to painless says to tap that wire into the clutch 12v side, pin b. which means 12v. ive applied 12 v from the clutch side and the car doesnt idle any higher at all, still bogs down, and still dies. like i said, ive bumped the a/c on idle to 800, which is a noticable difference than 650. with hp tuners, i can turn on the clutch coil in vcm controls and no difference in idle.

C2 pin 43, the (pcm output) ground side of the clutch coil i get 14Kohmns when the (vcm controled) a/c clutch is off and 14ohmns when on. i've checked out a 2nd car, with a painless harness and his computer has the same ohmn reading. in painless' harness the C2 11 low pressure signal is grounded to the chassis.
the ohmn reading were taken from that pin 43 to battery ground.
painless' harness also doesnt use a clutch relay, they assume that your using factory a/c wiring, and thats what im doing. ULTIMATE goal is to wire it through the relay so at WOT the a/c will cut off automatically, as it should.

as far as the request wire... i dunno, im still waiting for a friend to bring his 01 silverado to work so i can remove his high pressure switch (behind the compressor) and backprobe the wire and see what voltage it has.

from what ive been told by my electronics teacher is that from the schematic on the a/c controls (hvac) the signal should be ground. ive also tried ground, no idle difference.
any of that help, hopefully i didnt confuse you with that
thanks for the insite so far, hopefully we can come to a successfull conclusion!

The low pressure switch green wire goes to C2 pin 55 on the pcm and the other side goes to ground. But C2 pin 11 goes to the high pressure switch which controls the PCM and ground to chasis on the other side, it doesn't go to the low pressure switch. C2 pin 55 goes to the low pressure switch.

The A/C request signal should come from the HVAC module to pin 17 on the C2 connector on the PCM.

From the PCM C2 pin 43 should go to an A/C relay pin 85. (you need to concider installing a relay for things to work correctly. Pin 86 on the relay is hot with the ignition on and pin 30 hot at all times with 12 volts. Pin 87 on the relay should go to the green wire on the clutch.

The ground side of the clutch goes to a chasis ground on the back of the head and the low pressure switch can be tied into this same wire or the chasis.

Are you using the HP recirculation switch or not? I'm just trying to figure out which way you're going. Are you using the 87 A/C relay? I installed a 5.3 compressor on my LS1 using the LS1 controls. I plugged the back of the compressor and use the HP switch on the condensor to control the PCM. Are you going to delete any components out of the 5.3 system or adapt them to the 87?

[ZJM861]

all of your recommendations is my goal for this weend (installing the relay as per the diagram) and running a ground through my low pressure switch on the acumulator then to the computer, so it will match the schematic.

as far as the HP switch, no, it will be left out.

the relay will hopefully be installed with some temporary wiring this weekend and see if there is any change, which i doubt since the painless wiring harness does not have a wire in on c2 pin 43. my deal is the a/c request and why its not bumping the idle up? i want the pcm to do all the work, i dont want an actuator under the throttle like a carb setup.. theres someting im missing, and between this board and some tinkering ... its sure to get corrected.
clint

[Nitrous]

I guess what's got me is the reference signal to the pcm. Most reference signals come off of the HP switch or the switch on the condensor which usually has 3 wires. The schematic you have shows a white reference wire from the HVAC module to the DLC. If you have access to AllData take a look at the 03 schematic, it's closer to the F-body setup which I'm running. I can go into the PID's under "system" and bring up the A/C pressure switch to see what type of voltage it has. It has to stay a little above 1 to keep from tripping a DTC which won't let the PCM engage the clutch without reseting it. If you have low freon the switch will set a code also. I can't see the pcm working correctly without this switch and I don't see it in your schematic.

[ZJM861]

i have a schematic for an 03 silverado, but the pcm (parameters) will be different no? hopefully i can crawl under my friends truck tomarrow after work and probe the hp switch connector and see what type of signal its getting, and then try and replicate it on mine and see what the computer does.
i have a question for you about settings.... if for example a stock sivlerado and everything, the a/c belt is off and you turn the a/c on, the clutch engauges, will the rpm increase even though its not putting a load on the engine? what im trying to get at is will you hear the rpm change when the pcm gets the signal from the a/c button.
thanks,
clint

[Nitrous]

It'll decrease rpm and then the pcm will take over. My RPM pretty much stays the same with the clutch engaged but my idle is more consistant to where you can't here the cam as much. You can adjust idle/rpm with HPtuners once you get everything working. With the ignition on and the engine "off" you should be able to hear the clutch engage. The reason for installing a relay is to prevent a voltage spike which could damage the pcm or circuit components. I don't know why GM changed the A/C design on certain applications like yours when they could keep it simple like the F-bodies and vettes.

[Nitrous]

The more I read up and study this schematic I'm pretty sure you'll need the PCM to see RPM and will have to have freon in the system or jumpers to bypass the switches. The clutch will not engage with just the key in the on position. Once the PCM sees request and RPM it'll ground the relay and should kick in if you wire the system like the schematic.

Good Luck!

[ZJM861]

in your app, does your signal wire have voltage applied to it or ground? im stillwaiting for my friend to come through and bring his truck to work so i can probe it. i had some free time to fine tune my a/c so the pressures are spot on. .. im just lacking the a/c request... he said tomarrow would be good for him.. so hopefully i can back probe the connector to see what kinda signal this is needing.
by the way, thank you for your help and replies nitrous,
clint

[Nitrous]

I run an F-Body PCM so it has a 3 wire pressure switch on the condensor. A grey 5 volt reference, a black ground and a red and black wire which senses voltage at the pressure switch which sets a DTC in the PCM which has to be reset depending on high or low voltage. The setup you have is failry simple and just goes to ground from the PCM. If you set it up just like the 02 schematic it should work. If you use an 03 schematic the wiring changes and looks like the F-body. Since you already have the 02 setup I wouldn't invest in wiring and switches, just keep it like it is.

[ZJM861]

alright, my friend finally brought his truck and i crawled under it and removed the a/c high pressure switch from the back of the compressor, removed it and had him turn the compressor on. one had 13.~ volts (battery) the other had nothing... i got all excited and forgot to tell him to turn the a/c off to see if that was the signal from the control.
i bet it is, i doubt the computer will have 12v going from the computer, through the sensor and getting ground controlled by the button.. sob.. he will be bringing his truck again tomarrow and im gona do some exhuast work.. il just crawl back under there.. doh
clint

[ZJM861]

ok, so just like many things in this world, things dont happen when you want it to. i say this because when i wired in a relay to use the a/c ground controlled output, and powered up the a/c request wire, it took a few seconds then came one..i'd liked to kick my self in the arse... this whole time i thought i hurt the computer i didnt, i just didnt understand why it didnt happen the instant i gave red 17 power. so, its all good at the momnet! thanks nitrous.
clint

[Nitrous]

Glad things are going your way Clint!

[PitchblackC3]

I am trying to use a 2003 Silverado harness for a swap and I have run into a problem with the AC request signal. According to my schematics the AC request from the original silverado HVAC unit operates on serial data. How did you get it to work off a 12v signal.
I really been racking my brain trying to figure out a way to signal the PCM without the serial data. Seems like you did it.

*nevermind I overlooked where you said it was a 2002 harness that you used*