hey, i'm almost positive this will work, i removed my non functional a/c awhille ago, and wondered if i could use the a/c on and off temps in 6e to make a fan switch of sorts out of my now non funtional a/c controll on the dash. i.e. fan turn on temps could be set as i have them at 200 turn on and 185 off with a/c off, but set to 160* on and 150* off for dragstrip duty, so that when a/c is requested i can keep the hood popped and the fans on in the lanes to get her down to 160 where my thermo opens, i know the fans can do this with the hood open i've sat in the lanes for 15 minutes and had the car at 160* on the line. do able? issue? thoughts? thanks. ---------- oh also what should my fan switch be set to in arap if the ac isn't in there anymore? should i reverse the typical logic? the fan doesn't turn on at startup sooo,,, wow brain freeze..

Sounds like a plan. Give it a try and let us know how it works for you. That's how we learn here...get an idea, try it and report it.

If you do some searching on fan control with the $8D, I made a post where I found that reversing the operation (ie. set temps so Fan2 comes on before Fan1 and Fan1 turns off before Fan2) gave better overall cooling; especially when the A/C was on (which still used Fan1).

my other fan works constantly, the connector got heat soaked and i snapped it off= constantly have one fan running.

okee dokey off to test, but that normally open fan request thing, which way should i have it? normally you switch it when you go to ARAP with a pre 89 car, but mine has a/c removed so it's perpetually open, sooo will this even work? will the ecm know if a/c is on? i'll let you know what happened tommorow.

On the '165 with $6E, pin D11 is the A/C pressure switch input. This is used by the ECM to control the one fan. Not sure if you need to open or ground that wire to turn on the fan.

RBob.

As an "educational test" this spring, I tried to see if I could use my own inputs and outputs on the '165 to do something similar to what you're attempting. It was very simple and went something like this:

While TPS > 3.2 V (approximately 70% accelerator pedal), turn off the air conditioning and turn on cooling fans. As soon as TPS < 3.2 V, keep AC disabled and fans on for about fifteen seconds. Then, return everything to normal.

The fans were easily controlled using existing memory addresses, but I used an extra ECM output for the AC signal. On the '165, the AC compressor is controlled by a pressure switch, NOT the ECM (the ECM only knows the status of the AC). My final plan was to use a separate output to control a relay inline with the pressure switch, effectively cutting the AC signal when the ECM deemed it appropriate.

It's all very simple to do, but you need to know where to put the code. IIRC, I deleted the EGR loop and stuck it there. It was only about 32 bytes worth of actual code. The rest were all NOPs ("no operation").

yep i didn't even burn a chip, because i could never get the ecm to realize a/c was on. no matter what the hvac was set to, it would never say a/c requested or a/c on. therefor i would deem it useless to have seperate temps until we can tell the ecm a/c is requested. there is that pressure switch however the ecm is somehow in the loop or why the constants that are changeable and related to that (a/c on vs a/c off temps).

i tried jumpering my unhooked a/c stuff and nothing happened.couldn't close a circuit for some reason, did however get my washer fluid warning to come on as i tried assorted disvonnected connectors

an interesting thing, i was working around the ecm and jiggled my moates adapter, if i touch pins on the part that connects to the netres, i can manually raise the idle, i.e. i touch the right two pins on the right side of the board, and the idle goes up, don't sound right to me but fingers ain't supposed to be in there anyways, dunno what to think of it.

any idea why i can't get /ac to come on in the flags??

Need to set pin B8 into the ECM high. +12 volts is OK as it is the signal from the A/C clutch. This tells the ECM that the compressor is active. Raises idle speed and such.

RBob.

i see what your saying but could i supply that voltage conveniantly from a source in the engine bay so that it is switched by the ac buttons, perhaps a relay? trying to keep this a simple mod.

there must be a relay inside the compressor then correct? or does it recieve voltage from one of the two connectors? trying to understand this whole system of how the ac turns on i guess.

Maybe I can help with the wiring end of it. I don't know what year you have, but GM hasn't changed the colors much on these. A/C control head has a lt. green wire coming from terminal "c" that sends 12v to the pressure cycling switch(terminal b). It leaves the pressure cycling switch as a lt. blue wire (terminal a) and goes into the A/C high pressure (terminal a). It leaves the high pressure switch on terminal B as a dk green/white wire. The dk. green/white wire goes to a junction and becomes a dk. green which goes to the a/c clutch and also terminal B8 in connector C1 at the ecm.
So both switches need to be jumpered to get the 12volts to the ecm.
attached is a diagram.
Randy

so simply cut each connector and solder the wires together? what to do then with the diode? sorry if it seems i need spoonfed, i do, wiring and wiring diagrams aren't my forte

rockit,
You could cut off the connectors if you wish to never return it to stock.
That would work fine. We will probably kick ourselves 20 years down the road when these cars are like the 67-69 are now, rare!
The old clutch connector with the diode can be removed. The dk. green wire that goes to it is already split off in the harness to the ecm. That is what sends the signal which will get the flag to turn on. The rest of the settings in the bin are beyond me. Hopefully someone else can help us here.
Randy

i've had that thought myself about the future value, when the gta came out everyone said "collectors car!" guess what, no one knows what they are now... and how many 69's do you see sell for more because they still have the ungodly huge compressors? It's not the comfort options that make these cars classic, it's a rumble, an adrenaline rush, some action we got in the rear seat, a race we didn't think we could win, that's what we buy are the experiences we have in these cars, any weenie that would trade all that for "all original numbers matching" can just pass on buying any one of my cars.. not that any are leaving, as of yesterday i hit ten thirdgens in 5 years, 4 of which ran, and 5 of which i payed for got a 85 gta clone in bright red with t tops for 700 and she's truly rust/collision free.

oh and rbob it shouldn't matter about grounded or open on the head switch, just use the flag, n/o fan request, correct no?

What you are attempting should work.

One thing to note: The A/C on fan settings are always used below 11 mph with default tuning.

If you reduce the A/C on values below your normal settings, your fan will run at the reduced settings at all times when below 11 mph with both the A/C on and A/C off. This may cause you some confusion unless you are aware of what is happening.

This is an effective method for disabling the fans above a desired speed, since the increased A/C off settings will be used once you cross the 11 mph speed threshold.

The fan will continue to run for 15 seconds (minimum on time) after the coolant temp goes below the off temperature, or the off temperature goes above the coolant temp above 11 mph.

The A/C switch can also be turned on at any time above 11 mph, if additional cooling at speed is desired.

No wiring changes should be required.

In my case, I use this approach to turn off my fan 2 seconds after I exceed 5 mph. At which point my elevated A/C off settings come into play.

i'm trying to digest that still the reason the wiring needs to be change is because i removed my a/c compressor, therefore whether i press the ac button or not, the ecm can't see that a/c is on, which messes up my plan.
i turned that minumum mph to 0 in my tune to avoid any hassles as this was originally concieved as a way to control the fans without rigging up a switch.

Right.

The ecm needs to see the AC on and/or AC requested flags for this to work.

In my car, I can still see that these flags are set when the A/C switch on the dash is on, even with the compressor clutch disconnected.

Sounds like your not getting the A/C switch input on B8, as described below.so you will need to correct this.

Looks like you've got a handle on it.

In the event you don't get the a/c switch input working, you could always just use the existing vehicle speed function like I have described.

Since you're likely to be at very low speeds while waiting in the staging lanes, you can use the A/C on settings below say 5 mph, and revert to normal settings above like I have done. With a short minimum on time you can cut the fans quickly after launch, saving some parasitic losses during the run.

With this method your fan will be running also at stoplights, etc. but since you already have one fan running full time, I wouldn't think this would be too objectionable.

thanks for the input i appreciate all the help, soon as i have a chance i'm going to organize this info, get it to work and post up a guide for it, i'm sure i'm not the only one with his a/c removed that could use it.