A/C without computer control

[stargaazer7467]

looking for a way to control the air conditioner outside of PCM control

application-
3400 turbo install in my 95 sunfire, using N body wiring harness with a mote carlo PCM due to VATs issues.

since the car will not have the interior harness from the n car there will be no BCM, therefore nor class 2 signal from teh bcm to trigger the ac request. Has anyone ever ran an ac system "stand alone"?

Im looking at using a universal trinary pressure switch to comtrol compressor cut out and fan control but have yet to find anyone who has done it yet. I would love to allow the pcm to control it but have yet to find a way to do it.

or am i over thinking it? will the computer notice the idle load and step up the IAC to compensate on its own?

thanks for any help/suggestions.

[robertisaar]

i'll have to take a look at the wiring diagrams to confirm it, but there SHOULD be a signal that comes from the HVAC switch that would normally go to the BCM, it's likely that you could simply route that out to the PCM to have it control the A/C from there.

is there anything else A/C related that's missing? in terms of things the PCM interacts with, should be compressor(and it's diode), relay, 1 3-wire pressure sensor and the signal from the HVAC unit.

the PCM WOULD compensate for the A/C load, but it wouldn't be able to pre-emptively start compensating for it before it turns on, instead it would all be done as a reaction to the idle change. would definitely cause idle dips/surges when turning on and off.

[stargaazer7467]

there is a 12v signal thats normally switched from the control head to the BCM but not 12v input at the PCM, just class 2 data.

[robertisaar]

what PCM? you mention monte carlo, but no year.

[stargaazer7467]

oh sorry, going to be using a 98 monte carlo pcm.

[robertisaar]

okay, took a look, the 95 J-bodies did start using a lot of intercommunication instead of discrete signals.... luckily, it looks like you can intercept it and use it for your own purposes though.

95 sunbird: http://i.imgur.com/1Yt6uWI.png

the signal between the IPC and HVAC unit is 0V when not requesting the compressor and 12V when requesting the compressor, this exact scheme is used on the monte carlo PCM as well. could just simply bypass the connection to the IPC and conversion into the datastream and run that signal wire to the PCM. do you know what pin you'll need to hook it to?

[stargaazer7467]

how would i convert this signal since i cant apply 12v to the data wire? im sure i could just use that signal to trigger the relay but it wouldnt be a very smooth engaugement im sure. since it wuld have to compensate by reaction to idle drop instead of know it beforehand.

[robertisaar]

why is anything being converted? just use that 12V signal and run it to the pin on the PCM that's used for A/C request, it will work exactly like factory.

[stargaazer7467]

well in the wiring diagrams the 12v request signal is applied to the I/P from the HVAC head, then its sent to the PCM via the data line. I am lacking the pin out diagrams for the 98 monte carlo PCM, is there a 12v direct request signal to the PCM?

[robertisaar]

yes, nearly everything GM ever made with ECM/PCM control without a BCM(and even some with) use a scheme like that.

http://i.imgur.com/WZ8W12D.png

that's a 98 MC diagram.

[stargaazer7467]

man, i am very happy to see that! You wouldnt happen to have the PCM pinout diagrams do you?

[robertisaar]

http://imgur.com/VHu12HJ,c2r9SXs,9EzxQVA,6pil9fF,q9fpUJg,JM0jQfQ

[stargaazer7467]

thank you so much! now once the PCm get back from Milzy i should be good to go. i wonder if the uart line will run my cluster.