LT1 AC PCM Programming

[Bartman]

I have a complete Vintage Air installation on my LT1 equipped 240Z and it currently is not connected to the PCM. I would like to somehow let the PCM know to increase the RPMs when I turn on the AC without having the PCM check everything else (like AC pressure and temperature). My system checks everything else on its own and has a safety switch already installed.

 

So I'd like to wire in the AC request feed to the PCM without connecting all the other AC lines and still have the PCM think that it can energize the AC clutch.

 

P.S. - I have TunerCat

[dat240zg]

Did you "edit" your harness originally or was it speartech/etc? I guess it'd be a pain in the butt to remove it, but if it were a speartech harness, it seems like John could add that back in for you fairly easily.

 

BTW, ignorant question coming, after the initial tuning of the pcm, what's the advantage to using the tunercat? Is it more for further tuning after other changes?

 

Bryan

[Bartman]

Did you "edit" your harness originally or was it speartech/etc? I guess it'd be a pain in the butt to remove it' date=' but if it were a speartech harness, it seems like John could add that back in for you fairly easily.

 

BTW, ignorant question coming, after the initial tuning of the pcm, what's the advantage to using the tunercat? Is it more for further tuning after other changes?

 

Bryan[/quote']The harness was modified by the previous owner. I have the Factory Service Manual and I can find the proper connections and wire my Vintage Air into the PCM if it makes sense to do so. The only thing I want the PCM to do is to increase the idle when the AC is turned on, but in order for it to do that it wants to check the AC temperature and pressure. If I can't "fake" the system into thinking that the AC temperature and pressure are within the proper operating parameters it may not be worth it. My Vintage Air unit can already handle the temperature and pressure and I don't need the PCM to do that as well.

 

I found a post somewhere else where someone asked a similar question and the answer he got back was that its probably not worth it to connect to the PCM just to increase the idle speed. He thought it was better just to increase your regular idle speed enough so that it can handle the extra load when the AC is turned on.

 

My idle speed is already pretty low, so if I go this route I still need to figure out how to increase my idle speed with TunerCat.

 

As far as the use of TunerCat, it can be used to reprogram everything or just a small change. So in my case I could read the PCM, change one or two parameters and write it back.

[drexel_j]

There is one wire that you need in your wiring harness that connects to your compressor lead (when the compressor is on it sends a signal to the computer) and then if your computer is propgrammed to recieve the siginal it will increase the idle.

[Bartman]

There is one wire that you need in your wiring harness that connects to your compressor lead (when the compressor is on it sends a signal to the computer) and then if your computer is propgrammed to recieve the siginal it will increase the idle.

I appreciate the reply, but thats not quite how it works. The AC request tells the PCM that the AC is turned "on" and the PCM will adjust RPM and energize the AC clutch output only if certain criteria are met. The criteria have to do with coolant temperature, evaporator temperature, battery voltage, engine RPM, and AC system pressure. The problem for me is the PCM has no idea what the evaporator temperature or system pressure values are. Remember my AC system is a Vintage Air system and it monitors these items itself.

 

If I can program in values for the evaporator temperature and AC system pressure then I'll hook the input line to the AC Request B1 and take the output from the AC clutch control. D8. Then the engine will adjust engine RPM before sending the signal out the AC clutch control output.

[80LS1T]

I tried to see if the LT1 has a power steering pressure sensor but the diagrams I'm looking at from "Alldata online" aren't showing one. The PCM will also bump up the idle when it sees more pressure on from that sensor. If the LT1 has one (and your not using it) you could wire it in so that when you turn the A/C on it sends power or ground(which ever the PCM wants to see) to the PCM to trick it into thinking the wheel is cranked. You wouldn't have to trick any of the A/C signals then.

 

I'll keep looking at my diagrams to see if I can find it. You should be able to find out if you have a factory service manual pretty easy.

 

Guy

[Bartman]

I tried to see if the LT1 has a power steering pressure sensor but the diagrams I'm looking at from "Alldata online" aren't showing one. The PCM will also bump up the idle when it sees more pressure on from that sensor. If the LT1 has one (and your not using it) you could wire it in so that when you turn the A/C on it sends power or ground(which ever the PCM wants to see) to the PCM to trick it into thinking the wheel is cranked. You wouldn't have to trick any of the A/C signals then.

 

I'll keep looking at my diagrams to see if I can find it. You should be able to find out if you have a factory service manual pretty easy.

 

Guy

I looked in my FSM, but I couldn't find any mention of a power steering pressure sensor. If it has one that sounds like it would be a good possible solution.

 

I found somehting else in the FSM that may work. There is supposed to be a +5 volt reference at the AC evaporator sensor. If it's not present the AC clutch is supposed to be engaged at all times when AC is requested.

 

So if I'm understanding this correctly all I have to do is find an AC evaporator sensor and hook it up without the +5 volt reference.