AC wiring

[FAKKY]

Trying to understand wiring (AC) generallly but also specific to my setup.
I have a truck GENIII blue/green harness depinned as per LT1swap.
I have the fuse panel from bp automotive here. Has a 2 fans relay, 1 AC relay.

https://www.bp-automotive.com/produc...i-24x-engines/

I bought a coldmaster AC unit (local to me) with a Vintage Air compressor. 2 wire binary Pressure switch on the drier.
I have a puller fan on the radiator
I have a pusher fan on the condensor.

Just going to deal with non PCM controlled to begin with.

Under this scenario I think it would go like this.

Battery +12v => Pin 30 on relay
Drier Pressure switch => Pin 86 on relay (other wire on switch goes to Evap Unit in car). Grounded. 12v+ from ign on other wire.
Ground -> Pin 85 on relay
+12v feed to both AC compressor and condensor fan -> Pin 85

So basically the FAN and the Compressor get power in a NC relay ..... unless the high pressure switch kicks in ... and then the circuit is open and power to fan and compressor is stopped.


Right so far ?
=========================
So here's where it gets a little (more) confusing for me. Due to the BP automotive harness. And main puller fan.
The harness has the following wired to main harness (which was done about 1 year ago).

12v AC compressor (Green) thicker wire
#1 FAN relay dark green (12v for FAN low speed)
#2 FAN relay dark blue (12v for FAN high speed)

Smaller AC request wire (green/white) 12v to engage A/C compressor
Smaller gage AC relay control ground wire (black/white).
Smaller gauge Fan #2 wire (blue)

Instructions on this from BPAUTO say.
1) Ground AC relay control wire.
2) Hook AC request wire to your AC control unit in CAB to power AC.
3) AC compressor wire to compressor.

--- Nothing about FANS. Im guessing thats because the two FAN relays are wired for PCM control ? So better to go that route ?

Trying to understand best way to "merge" the two harnesses so to speak.

[ls1nova71]

I can get you ice cold air in your vehicle in 2 easy steps....

1-Move to where I live.
2-Roll down the windows.
Done!

But seriously, you need a trinary switch in place of the binary switch to run electric fans. Not sure how BP says to hook up an AC request wire since most blue/green harnesses don't have that, and only some PCM's will accept it.

[FAKKY]

Sorry - to the side.

[FAKKY]

So with a Trinary switch .... independent of PCM (standalone) ... wire like this to control AC and Condensor fan.
https://www.vintageair.com/universit...rinary-switch/

Then for main radiator fan - just run that off PCM FAN#1 relay ........and enable at say 140 degrees to tun on. I think its just a single speed fan.

Sound right ?

[ls1nova71]

Yes, that sounds about right as far as the trinary wiring goes, but I wouldn't have the cooling fan come on so early or the fan will be on a lot.

[FAKKY]

Thanks.
Then have the trinary setup from VA wiring for controlling AC and condensor fan standalone.

Then since i have the PCM DIY FAN relays kit from BP auto .... might as well use that FAN1# relay for PCM controlled main radiator fan .... say 180 degrees ?

Understanding correct ?

[ls1nova71]

That should do it.

[FAKKY]

Originally Posted by ls1nova71

That should do it.

Thx boss man

[FAKKY]

Nova ......
Whats the advantage of the trinary switch setup, I mean I get it if just running 1 fan so you have seperate control for both AC and for engine temp.

Can you just run it with binary switch in the format of ...

1) AC and Condensor FAN come on anytime AC is turned on in CAB. Cuts out by pressure switch.

2) Engine (coolant) Fan is hooked via PCM to internal engine temp in harness.


Seems like this would be just as simple if not more so - and as effective.

[plumber452]

I recently purchased the same harness from BP Automotive and after some lengthy searches I've found that from 03 on up the Green/Blue connectors PCM do not have an A/C request. The PCM receives its signal through a serial data line coming from the A/C Heat switch module in the dash of the original donor vehicle. It appears most people are wiring it like LS1 Nova recommends. I've read other threads where people have "Stuck" an A/C Switch module, like the one that came from the donor vehicle, under the dash and run their new A/C system through the module and out to the PCM. This way it maintains the PCM control of the fans etc. Good luck and keep us posted.

[FAKKY]

Originally Posted by plumber452

I recently purchased the same harness from BP Automotive and after some lengthy searches I've found that from 03 on up the Green/Blue connectors PCM do not have an A/C request. The PCM receives its signal through a serial data line coming from the A/C Heat switch module in the dash of the original donor vehicle. It appears most people are wiring it like LS1 Nova recommends. I've read other threads where people have "Stuck" an A/C Switch module, like the one that came from the donor vehicle, under the dash and run their new A/C system through the module and out to the PCM. This way it maintains the PCM control of the fans etc. Good luck and keep us posted.

Thanks.

I did see that here.

https://www.bp-automotive.com/air-conditioning-faq/

But honestly when I bought both the truck harness (21 circuit) and BP fuse block harness I didnt know how it all worked .... and really its overkill for what I need on the truck. Read that the factory AC is done through serial data .....

No idea why the kit I bought says "A/C Compressor Relay" .... when really they are saying the request/ac wiring should be a seperate harness.

Oh well .... moving on.
Thx all.

[plumber452]

I understand. As my name, Plumber 452, should tell you all you need to know about me, I'm a Plumber "Retired" so wiring is not my strong suit. I'm going to get a A/C module and go that route.I'm trying to get this all ironed out before I install the engine/trans combo. I'll keep everyone updated as to how it works out. I do have the GM schematic for the A/C Heat module and how it ties into the PCM, if you would like to see it.

[ls1nova71]

Originally Posted by FAKKY

Nova ......
Whats the advantage of the trinary switch setup, I mean I get it if just running 1 fan so you have seperate control for both AC and for engine temp.

Can you just run it with binary switch in the format of ...

1) AC and Condensor FAN come on anytime AC is turned on in CAB. Cuts out by pressure switch.

A binary switch will just cut the power to the compressor if the head pressure gets too high, or too low. If you just use that and have the fan come on any time the A/C is on, the fan will run all the time. You don't want to hook the fan to the same wire as the compressor, because if you did that, when the head pressure got high enough to cut out the compressor, it would also cut the fan, the exact time you need it the most.

With a trinary switch, when the pressures are low enough, the fan will shut off, such as when moving down the highway. You will have sufficient air flow over the condenser at that time so fans won't be needed.

[FAKKY]

Originally Posted by plumber452

I understand. As my name, Plumber 452, should tell you all you need to know about me, I'm a Plumber "Retired" so wiring is not my strong suit. I'm going to get a A/C module and go that route.I'm trying to get this all ironed out before I install the engine/trans combo. I'll keep everyone updated as to how it works out. I do have the GM schematic for the A/C Heat module and how it ties into the PCM, if you would like to see it.

Right.
Well working in IT/computer software doesnt help me with wiring or wrenching. So we are both hosed ....... luckily we have Nova (and others) here who have that knowledge and ARE willing to share.

[FAKKY]

Originally Posted by ls1nova71

A binary switch will just cut the power to the compressor if the head pressure gets too high, or too low. If you just use that and have the fan come on any time the A/C is on, the fan will run all the time. You don't want to hook the fan to the same wire as the compressor, because if you did that, when the head pressure got high enough to cut out the compressor, it would also cut the fan, the exact time you need it the most.

With a trinary switch, when the pressures are low enough, the fan will shut off, such as when moving down the highway. You will have sufficient air flow over the condenser at that time so fans won't be needed.

Dammit - thats why you get paid the big bucks. Forgot to factor in actually how AC works .... juts been thinking of wiring.

Funny though -- this is literally the manual from the AC company - both fan and compessor wired together.

[rocketmench]

Hi all, I realize this is an older thread, but I thought I'd post an update regarding how those 2003+ Blue/Green P59 PCMs that do not accept analog 12V signal for A/C request can be modified to accept that signal. I'm going to be restoring a 1968 K20 and I want to have analog A/C with my LS swap also.

In summary, I obtained two PCM's to compare; one that had the IAC stepper control mosfets and A/C request circuitry, and one that did not. I traced out the circuit at pin C2 17, where the A/C request signal is sent. On the PCM that can accept this signal, there is a pull-down resistor and debounce (low-pass filter) resister/capacitor combo that is missing in non analog A/C request PCMs. I verified that when these components are soldered into the board, the PCM responds to analog A/C request. And fans 1 and 2 can be made to come on as well if using the Analog mode in the OS.

I posted the details of which resistors and capacitors to add in a post over at ls1tech.com:

https://ls1tech.com/forums/conversio...c-request.html

Hope this helps.

[ls1nova71]

Originally Posted by rocketmench

Hi all, I realize this is an older thread, but I thought I'd post an update regarding how those 2003+ Blue/Green P59 PCMs that do not accept analog 12V signal for A/C request can be modified to accept that signal. I'm going to be restoring a 1968 K20 and I want to have analog A/C with my LS swap also.

In summary, I obtained two PCM's to compare; one that had the IAC stepper control mosfets and A/C request circuitry, and one that did not. I traced out the circuit at pin C2 17, where the A/C request signal is sent. On the PCM that can accept this signal, there is a pull-down resistor and debounce (low-pass filter) resister/capacitor combo that is missing in non analog A/C request PCMs. I verified that when these components are soldered into the board, the PCM responds to analog A/C request. And fans 1 and 2 can be made to come on as well if using the Analog mode in the OS.

I posted the details of which resistors and capacitors to add in a post over at ls1tech.com:

https://ls1tech.com/forums/conversio...c-request.html

Hope this helps.

I just read your thread on LS1Tech, and I'll give credit where credit is due, that's pretty impressive. You are obviously more of an electrical engineer than I am, because there's no way I would have ever figured that out. I think the downside is that most people without your knowledge and soldering capabilities will do more damage to their PCM than good trying to add those small parts.

So did you still have to change the A/C request to 'analog cycling' in the tune? I assume that's what you used the Tunerpro for?

I'm not knocking your work, but it still is probably still a little easier for most people to just find a PCM with IAC drivers and just reprogram that to make it work if PCM controlled A/C is a must for them.

[rocketmench]

Thank you LS1Nova! I've been a lurker for some years now as I plan my restoration project, and your posts are always helpful.

I set the A/C request mode to "Analog", I did not try "Analog Cycling". As I understand it, "Analog" mode requires a pressure sensor in the A/C line which controls a continuously running variable displacement compressor, as opposed to a simple pressure switch for the "Analog Cycling" mode which presumably uses a fixed displacement compressor that is switched on and off.

To emulate the pressure sensor with the appropriate pressure reading, you can either add a roughly 70-80 kohm resistor between I believe C2 14 and C1 45, which creates a voltage of about 2.5-2.6V at the C2 14 (the resistor acts as a voltage divider with the roughly 70kohm internal resistor at C2 14), or just directly input a voltage at C2 14. I did the latter.

As for difficulty level of the actual soldering, I was expecting worse. Using a basic soldering iron with a reasonably small tip, it was not too difficult to remove the one resistor, and add the necessary components. Taking care to use flux and basic good soldering techniques was all I needed. I did this on 2 pcm's without problems.

The coolest part was in observing Fan 1 come on a soon as I applied the 12V to C2 17 to request the A/C! Also, adjusting the potentiometer to change the emulated coolant temperature, I could cycle Fan 1 and 2 on and off at will.