Standalone A/C... Possible?

[Blackhat]

1989 240sx w/ KA24E

Does anyone know if it's possible to wire the A/C to not relay through the ECU and have it be a standalone system? I've been adapting over to a MSEFI setup and been looking at the Thermal Amp and A/C relay lines thinking that just maybe I could do something there besides leaving the ECU to take up space. Any ideas?

As a side note, don't suppose anyone could give me insight into pin 43? I had no clue there was a "Power Steering Pres. Sw.". Is there some sort of monitor for the Power Steering system in the ECU?

[TKfoshori]

it could be the power steering wire that keeps your rpms up when your at full lock, but im not sure.

[twofourzerosx]

yeah i think it just changes the idle...the pressure switch is located on the drivers side frame rail IIRC

btw...nice choice going megasquirt. you building it urself? wat ignition system are you using? im gunna do MS-1 v. 3.0 on my sr20 next year.... running COP :) i dont know any1 else with it on the sr

[nrg]

The ECU does nothing to the AC system. When you hit the AC button on your heating/ac control panels, it just ground the pressure switch, then it tells the ecu that your AC is on, then it picks up your idle alittle. There are two wires on your ECU for the AC. the in and the out. you don't need those wires. Just build a relay that gets trigger by the AC button. The relay will ground the pressure switch and also power the IACV. That's pretty much it.

[projectRDM]

Bingo on both counts.

Power steering pressure switch just idles up the engine at full lock, ECU trips the FICD valve to open when the A/C is engaged. As long as you're keeping the thermo amp and triple pressure switch you're fine.

[Blackhat]

Well, first of all, thanks a TON for the anwsers. Zilvia.net is now my favorite 240 site :bow:

The MSEFI question, I'm using MS1 Cpu V3 board and plan on using MSnS-extra. Ignition is a MSD-6a w/ MSD coil. All the work was done when I built the MS. The MS just sends a signal for the coil to ignite to the MSD and then the MSD does the rest. I looked at COP, but couldn't justify it for my situation. Will you be using the Opto CAS or doing something like an EDIS setup? If you're going to use the Opto CAS just hit me up when you get to it, it's the same setup on all of the nissan opto CAS's so I can help you skip the headaches involved with that.

The A/C question. You'll have to forgive me, I am weak with my A/C system knowledge. I know the Thermo amp is part of the A/C system but not sure what needs to be done there. I was told a while back the ECU also had some control over the A/C for things like cutting the compressor while at WOT. That's hearsay so I'm not sure, but the only wires I found on the ECU for the A/C was the A/C relay and the Thermo amp. I feel comfortable just setting up the A/C relay off of the button on the A/C controls, but I need more info on what the Thermo amp is and what needs to be done with it.

The Power Steering Pres. Sw. Full lock? Sorry, never heard of that before... does that mean when the Power Steering is at full pressure? Like... turning the wheels while stopped? Does anyone see a problem if the car does not idle up when the Power steering is in full lock?

Thanks again for the help!!!

[projectRDM]

PS switch, idles up the engine when the steering is at full lock. Basically if you're sitting in the car and turn the wheel as far as humanly possible you'll see the tach dip for a second, the pressure switch then triggers the ECU to idle the engine back up to compensate for the added load. You don't need it, since you're rarely at full lock and the idle only drops a few hundred RPM if anything. Do a search in here, we've talked about it recently in a few other posts.

A/C, the thermo amp resides on the evaporator case. You don't need to mess with it at all. Only thing you're concerned with at the ECU is the FICD valve, it's part of the IACV and idles up the engine when the compressor is engaged. The triple pressure switch is what signals the ECU to cycle the compressor on/off, but that's mostly under heavy engine load or when the fan is at low speed. Trace through the FSM and you'll get a better idea of how it all works, but I think as long as you keep the FICD connected and just use one of the outputs to drive it (or use the A/C switch directly) you're fine.

[Blackhat]

Cool on the Power Steering Pres. Sw. That would have been a pita to setup.

The FICD is connected to the A/C relay. As long as the compressor is on (A/C relay is on) the FICD will automatically come on. Which is a life saver because I can only control one PWM valve with the MSEFI. So, as long as I setup the A/C relay switch to ground out the A/C relay wire you think I'd be golden?

That leads me to another point which I'll add in case anyone doing a MSEFI searches this message. The only idle valve you need to worry about is the AAC. The Air Reg just takes power from the Fuel Pump relay which starts heating up the element in it. Which slowly closes off the idle air flow (to my knowledge). Taking care of cold start idle. The FICD I already mentioned and the AAC has a frequency rating that I had at one time but lost. Don't suppose anyone has that info sitting near them? For the Frequency range the AAC takes for signal?

[twofourzerosx]

blackhat i can find out info for you soon on using the factory CAS to trigger megasquirt. my friend just got his turboed maxima running on MS2 using the stock dizzy. basicly it puts out a square wave... one wire sends it every 180* and anouther sends it every 1*...you just need to set the MSefi to recognize that signal. im not too familiar with teh softwear so i really cant help you out all that much. i believe you can modify the disk to use a second signal as a reset pulse, or maybe the factory disk has a longer slit or sumthing, i cant remember. i found this though:
http://www.autronic.com/page_files/trigger_disks.htm
http://megasquirt.sourceforge.net/extra/setup-wheel.html
its a wheel that allows you to use one wire as the 180 signal and one as the reset pulse.

good luck

[Blackhat]

Yeah, you get the 4 slot signal from the black/green wire. I suppose you could just knock out a hole in that line for a reset, but I think if the reset is necessary you'd be able to use the 360 slot signal. I believe I've seen where you can set the MS to recognize the slightly longer (cyl. #1 TDC) signal as cyl #1.

The CAS turns 1/2 speed of the crank. Which means each slots signals TDC for the spark event. (2 full turns of crank for all the cylinders to fire). The 360 is fairly useless as the MS will time out the distance between the 4 slot signals. MS2 can't even handle the 360 signal until they finish the new expansion board they're working on. But the 4 slot signals are 90* signals on the CAS, not sure where you got the 180* signal part, unless you're referencing to the crank. In which case the 360 signal is a 2* signal.

You can use the stock CAS wheel either way though. White out works well if you just want to close up all but a couple of the 360 slots... in which case you could make yourself something like a 36-1 tooth signal. Personally, I'm going for the 4 slot stock setup and just setup to recognize the longer square wave pulse as cyl. #1.

[twofourzerosx]

i got the 180* from the FSM...they always call that wire 180*...dont know why. i know what ur saying tho, and i know that my friend didnt change the disk, and he is only using one wire, so i think he did get MS to recognize the long slot for tdc

[Matt Cramer]

With a normal distributor type ignition, you will just use the four slots spaced 90 degrees apart - I believe the manual calls it the 180 degree signal because it gives a pulse for every 180 degrees of crank rotation. MSnS-E will trigger off the leading edge, and pretty much ignores the actual length of the slots.

You won't even use the 360 slots on the edge of the distributor, as Megasquirt uses a somewhat different timing calculation from what the Nissan ECU uses.

The wiring is very similar to the way you wire it up in our article on the 280ZX:

http://www.diyautotune.com/tech_articles/how_to_megasquirt_your_280zx_turbo.htm

For a 1989, even the wire colors are the same. I've been working on an article covering the specifics for the 240; it should be up pretty soon.

[twofourzerosx]

wooo matt you are on here? id dint know diy was on these forums

[Blackhat]

The pullup resistor for the CAS signal, can that be pulled from the same 12V that the CAS gets power from? or would that cause signal noise?

[Matt Cramer]

Should be OK to pull it from the CAS's source. The resistor's large enough that it will not create much, if any, noise.

[MegasquirtCA]

I say get rid of that POS Nissan electronics :), thats what I did and never looked back.

I wont even use the Nissan CAS when Megasquirt Router board comes just a straight up gangsta HALL sensor.


twofour theirs about 5 peeps running COP on their SR's using MSI and a dozen more running EDIS.