AC hook after after 5.3 conversion (1 Viewer)

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workingdog

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What is the best way to make the AC work after a SBC conversion?

From reading a little here, simply bypassing the AC controller to hardwire the compressor is a bad idea long term.

Should you, can you, use the ECM to power the compressor.

Or, is there another 'thing' I can use in place of the AC amplifier that will do the pressure and temperature control features without the idle control?

Peter
 
I supplied the old harness with a tach signal from the ECU to the old coil wire. That gives the AC amp and the tach harness a signal.

I also hooked up the old AC clutch wire directly to the GM ac clutch. Some have had to use a solenoid for this part since I think the new clutch draws more current and blows the fuse.

This way it is like stock, but with no AC idle up.
 
BTW, using the GM ECU to run the compressor takes a separate "box" that runs all the ac stuff in the GM setup, so it's not easy.
 
Thanks for the info.

I tried the method I read here of jumping the yellow wire in the AC controller to the black-white stipe wire but no joy - No 12v on the yellow wire when the AC button is pressed - should there be?
 
I'm working on the method described by rover.... or I should say my friend is...hopefully a/c working soon with 5.7 vortec. plan to use yota a/c compressor wire at the gm compressor though a relay. Then plan to feed neg side of coil with tach signal from ECM. New GM compressor and new TOyota dryer and the rest is toyota OEM stuff or Custom hoses. Also plan to install pusher fan in front of condensor but a/c work is first in line.
 
I apologize for being dense, but what do you mean connecting the 'neg side of coil with tach signal from ECM'. Do you mean I can use the tach signal from the ECM to fool the AC controller? Then use the compressor signal from the AC controller, through a relay to controll the compessor? The challenge will be finding those wires up under the dash.
 
There are two wires under the hood that feed teh coil (on your 2f engine) when you removed the 2f you should still have those wires. I use teh pos side wire to get a ign on signal that feeds to the GM ECM that tell its power on. I'm told from other sources that you can feed (my GM ECM wiring harness has a tach signal wire) the tach signal wire to the neg wire of the coil thus providing a signal to the ac amp that will cycle the compressor. Just for reference I have a 99 5.7 Vortec and I run a so called painless engine wiring harness.

Then you take the toyota OEM wire that conttrolled the OEM compressor and using a relay ...( the factory wire is the turn on signal) to power the GM compressor (cycle on / cycle off compressor.

I'm told this works, I'm in the process of proving if it does or not. I trust the source so I hope to have ac soon.

I'm talking about wires under the hood....the idea described above only invovles modifications to the toyota wiring harness under the hood.

I'm not an expert and I wanted to to control the A/c Cycling of the compressor with min modifications and through the factory controls. I should know within a few days if what I describe works. I've heard from multiple sources that it will.

My only real concern with the ac is controlling the cycling of the compressor. I don't want to hack up the inside wiring harness.

Also told that a disel ac amp will work without tach feed, but I don't know the manner in which it functions, other than I realize that the diesel does not have an electronic ign system and I htink the tach is a different style of animal
 
Thanks for the longer explanation. I don't think I have any of the stock harness under the hood, but I do have the tach signal from the ECM in the dash in the Howell harness. I assume the part where you hook the positive coil wire to the ECM has nothing do with AC, but tells the ECM the key is on - is that true? I take it the negative coil wire is connected to the AC controller as a tach input? I should be able to duplicate that. I have a new wire running from the AC controller to the compressor, but no relay, so I'll have to add that.

But to test that part of the system, I should be able to put +12v on the black-white strip wire under the dash going to the compressor and the compressor should engage. Then I need to connect the tach wire in the Howell harness in the dash to the tach input on the AC controller - anyone have any idea which wire that is?

Also, what else does the AC controller need to have working for the compressor output to engage. Does the pressure and temp sensors need to be connected?

Peter
 
yes the pos coil wire has nothing to do with teh a/c as I described...its giving the GM ECM an ign on signal so the ECM primes the fuel pump prepares for engine start (simple explanation).

Connecting the tach signal wire (from teh GM ECM) to the negative coil wire provides a tach signal...I'm not saying to do anything beyond that with this one connection.

re-read what I've written.... the tach signal wire from the ECM is providing the tach singal....thats why you connect it to the neg coil wire. The ac amp reads the tach signal...it does not generate a signal.

You need to check your toyota harness...surelly someone did not just go in and cut these main wires out of the harness.

Once again to the extent I know the old school toytoa setup has no way to know about the compressor head temp or pressure switch anywhere on the system. It would be good to have that stuff working where if pressure drops or head pressure gets to high then the compressor is disabled.

You really need to look at teh schematic of the ac amp and compressor control. I'm relating to you what I've read others discuss and talk about on the forum and in person.

I would not cut or alter any wires feeding the ac amp unless you have a full understanding of whats going on. I'm willing to gamble myself but I'm only modifing one circuit and that's the idea of feeding the neg coil wire with the tach signal off the ecm. Other than that I'm just using the factory wire to control the a/c compressor but have decided to place a relay at the end of the wire to allow greater voltage to feed the compressor on / off via the relay.

Don't go to cutting the wires and stuff just based on what I'm saying.... as I related above we are in process of making sure this works. I have an automotive background and so does my friend doing the work...so we take a measured approach and test things out first....ie connect stuff , check with a test light etc or whatever. We also would stop if things don't work as predicted and consult the shop manual., but the shop manual is only going to show or explain how the factory system works...and you'll have to tie that in with an understanding of how the GM compressor works.

You are in CA....while I"m not familiar with the locations without looking on the map I know that a number of guys with engine conversions have taken their junk to local shops to get the ac working. If you look through some of these threads by searching engine swaps you'll come up with some names, also sugguest you look in the clubhouse area for the toyota club that covers your area and post questions there. THere seem to be a lot more LC in CA and out west than here where I live. Basically around here you end up doing most things yourself or you and your buddies get together to figure things out.

Don't cut on the factory underdash harness or the ac amp harness unitl you understand more to do with the wiring...I'm only saying this as advice , not being smart@$$. I'm sure some of the LC guys in your area would be glad to offer help or advice on where to take your truck.

You still will have to get some custom hoses made up, you will have to charge with the freon of your choice, most likely will need ac oil added and o ring replacement too, and a new compressor and or toyota dryer too.
 
Thanks for that long response. I appreciate the information.

I wasn't suggesting that the AC Controller generated the singal. I'm trying to figure out which wire used to be the negative coil wire and how I can find it. There is not much left of the stock harness in the engine compartment. So finding the right wire will be the challenge. The tach signal is already in the cab from the Howell harness, so it may be easier to do the wiring inside.

peter
 
my truck is over at my friends house or I would post up some pics. When I get it back I'll post up. When I took my engine out we did not cut any wires excpet for a couple related to the emissions crap and where the coonector broke. I then used some little labels I got from Wal Mart (like price tags) with string to label the wires ...and even after numerous offroad trips the tags are legible, but I don't expect them to last much longer.

yes it mght be eaiser for you in the cab. My ECM is under the hood.
 
Why can I find a schematic of the AC Amplifier?

EDIT - found it. Page AC-3 of the Body and Chassis SUPPLEMENT

peter
 
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And to summarize what I've learned from searching. The three basic techniques for getting AC to work after a conversion.

1. Short the yellow wire to the black with white stripe wire at the AC Amplifier - but you will not get pressure or temperature control and the compressor will run continuously causing freezing up and unecessary wear on the compressor.
2. Run the tach output of the ECM to the black wire (coil input) of the AC amplifier and use a relay to operate the compressor output (black with white stripe).
3. Swap to a FJ62 AC amplifier ($50 used from SOR) which does not require a tach input. I assume you still need the relay on the output for this.

And, for those who've never had AC in a 60 before. To get power on the Yellow wire at the AC Amplifier you have to have the blue AC button pressed. And to get the AC button to light up and pass power through to the Amplifier you have the key to ON (Not ACC) and the FAN ON. Took me 20 minutes to figure that out.

Peter
 
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OK FYI... on my truck with has an engine from a 1999 GMC Yukon / 5.7

Two issues as of ths evening:

The block I had to adapt hoses to the A/c GM Compressor does not fit / seal correctly. There are a couple of variations and so I got to figure out which one works and get another one...block is from here.
Doc's Blocks Home

2nd issue is that we did mate the ecm tach signal wire with the neg coil wire under the hood. Observered the Factory tach working but no signal at the A/C clutch control wire under the hood. Have not had time to explore beyond that but assume on the right track as the factory tach appears to be working.

Got to figure out the correct adapter block or get a factory GM A/C chose or block and adapt from that.
 
From my looking at the wiring diagram, the wire that went to the tach is not the same one that fed the AC Amplifier. They both leave the negative coil, but each then takes a different route into the cab. Glad to hear the tach will work.

Peter
 
From my looking at the wiring diagram, the wire that went to the tach is not the same one that fed the AC Amplifier. They both leave the negative coil, but each then takes a different route into the cab. Glad to hear the tach will work.

Peter

that's why i wired the tach output of the ECU to my old coil - wire, it is where the harness got it's RPM signal originally.
 
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saw another related post... I need to go find my manual but if anyone knows...

On OEM FJ60 gas engine setup with A/C... Is there a safety built in where the compressor will not engage if low on freon? I assumed there was not but have not hunted through the shop manual. There are no pressure sensors on the a/c hoses under the hood that I can recall. I have a conversion over to V-8 now but I dont' recally seeing anyting like "low pressure switch" or other electronics on the A/C system when I took all of that out with the engine swap.
 
the low pressure switch and thermo switch are in the evaporator unit in the cab, they are wired to the stock AC amp.

Giving the AC amp the signal from the v8 tach output via the original negative coil wire dosen't bypass any of this stuff, in fact none of that stuff changes at all. That's why it will work like stock except for the AC idle up.. you'll loose that feature but with the v8 it does Ok without it since it's a big motor and does have some idle control no matter what. usually the revs don't drop low enough to let the compressor kick off. Also, even though the signal is not the same as a 6cyl motor it still works... you can use the blue knob on the AC amp to raise the cutoff so it works fine.

Getting an AC idle up to work with the v8 requires the ac module from the v8 (at least for the vortecs) it's not as simple as an input to the computer to drive it.. the vortec ac module does all the temp and low pressure control crap as well as the idle up plus other random stuff and feeds the computer to tell the motor what to do.
 
the low pressure switch and thermo switch are in the evaporator unit in the cab, they are wired to the stock AC amp.

Giving the AC amp the signal from the v8 tach output via the original negative coil wire dosen't bypass any of this stuff, in fact none of that stuff changes at all. That's why it will work like stock except for the AC idle up.. you'll loose that feature but with the v8 it does Ok without it since it's a big motor and does have some idle control no matter what. usually the revs don't drop low enough to let the compressor kick off. Also, even though the signal is not the same as a 6cyl motor it still works... you can use the blue knob on the AC amp to raise the cutoff so it works fine.

Getting an AC idle up to work with the v8 requires the ac module from the v8 (at least for the vortecs) it's not as simple as an input to the computer to drive it.. the vortec ac module does all the temp and low pressure control crap as well as the idle up plus other random stuff and feeds the computer to tell the motor what to do.

Ok...thanks for the feedback. I've got to figure out what a/c block to use or just go get some hoses made up and hack up the GM A/C hose assembly I have. A/C is on the very short list of crap to get done.

Not sure what is required on the 5.7 to get idle up feature to work. Obviously it would invole a signal to the ECM that A/C request was on or that the compressor was engaged. I would like to get that to work but that will be downstream of this. I don't recall any other magic items with my engine other than the cruise control module. I'll look into that later on and post up if I can get it to work.
 

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