Ultimate LSX AC Control Tutorial - HalfSpec Engineering

[wickedrx7]

I'm pretty sure you've diagnosed a bad AC compressor clutch. I'd have to dig through my PM's but I'm pretty sure this happened to 2-3 people years ago when I used to sell the kits. When the clutches fail they hard short which blows your fuse.
If you wanted to be completely sure, you could hotwire in something small to the compressor plug like a turn signal or a car horn or something like that. The idea being that you could turn on the device as if it was the compressor and you would know that the AC controller is supporting a normal load correctly.

For the RPM window switch... What engine and gauge set are you running this on again? Normal LS engines have a tach output of 2 pulses / rpm and is what I had all the switches I ordered from baker electronix programmed for. So a 4800 rpm signal would be a 9600 PPS (pulse-per-second) signal. If you have a XYZ PCM that sends out 4 pulses / rpm (normal in most other V8 applications), your PCM would send out a 9600 PPS signal at ~ 2400RPM. If that's the case, the only way I know around that is to have the RPM window switch reprogrammed (http://www.bakerelectronix.com/) for a 4 pulses / rev application or buy a end-user programmable window switch. Unfortunately, Baker Electronix is closing from what I've heard

Lane

Which AC compressor are you running?  I fried two clutches before realizing the pin out was flipped from previous years.  I am running a 2012 L99 accessories. 

[Negrok20r]

^^ I have a 2013 ls3 compressor

And after checking the lsx harness ac connector with a light bulb , it seemed that is supporting the load correctly.
Next,  I checked the compressor and wires are flipped.
I'll replace the clutch tomorrow and see how it goes.
Rpm signal Im running holley dominator aND it's set up at 4pps I think. Idk if I can change it to 2pps I'll see, if not I'll get a Dakota box to do it .
Thank you guys .

[ls3_rob]

Here is a new problem I noticed recently having used this kit just fine for 2 years now (using ls3 ac wiring kit with ls1 accessories and ls3 engine)

When the ac button is pushed the car at a stop will die or lose all electronics and when moving bucks like crazy/voltage fluctuates acts like it wants to die

The volts act like a bad alternator going from 14-8-10-12-14 back to 8 and the lights flicker and radio shuts off

I was driving around 10-15 miles and died/came back to life 4 times but only when ac was on. At a stoplight died completely

Already replaced ignition switch/battery/alternator to no avail

Problem stops when ac button is off

Already tried jumping the compressor connector to a light bulb and worked fine
Also tried jumping the pressure switch and compressor kicked on with no problems, ac clutch spins freely and all relays/fuses are good

No ideas at this point

[halfspec]

Does it make a difference if the compressor is unplugged? I.E. does it stall out when just the electronics are involved?
How about pulling the AC harness fuse?

You've done a good job starting to isolate the problem, but the two things above might help clarify the problem even more.

Lane

[ls3_rob]

Unfortunately, neither unplugging the AC fuse nor the compressor do anything to help the issue.

What I mean by that is everything voltage-wise stays normal except for the working AC of course.

I have attached some videos of the problem with everything plugged in and working as it has for the past 2 years.

Like I mentioned voltage will drop and even sometimes die. Ac is still cold and both fans blow as well as the AC clutch spin freely.

This problem happens intermittenely and not every time the button is pushed.

I do appreciate any ideas or help at this point.

Links of videos below:

[halfspec]

Is that your radiator fan I hear kicking on every time you press the AC button? I mean, that's normal, it's just surprisingly loud to me. If so does your car behave the same way with the fans unplugged?

The only reason I ask is because I looks like you're browning out a cabin or lighting circuit (maybe your tns circuit) with a large transit load, which in this case may be your radiator fan depending on how you supplied power to it.

Lane

[ls3_rob]

I have it wired exactly like this: The unplugging of fan relays made the problem stop

[ls3_rob]

I unplugged all factory fd fan relays in the passenger fender well would that be a problem?

[halfspec]

Removing the stock fan relays wouldn't cause this issue. I'm more concerned with how you powered your relays and it may partly be my fault due to the diagram I created. Specifically, the fan relay's really don't need switched 12V to operate correctly. Getting 50 amps of switched 12V is where I think the issue is as that's a tall order for even the ignition switch. I don't know where you decided to get that kind of power, but I would bet it's overtaxing where you tapped.

Consider this revised diagram:



The important bit being, that for a 50A load, you really need to go back to the battery directly, using 12Awg for each of the two fan relays.
You might give it a shot with temp wiring if that's easier, just to prove that's the issue, before you actually do it for real. Unless you're one of those nuts running a motorcycle battery or something, I think that should solve the problem.

If that's the issue, you have my apologies for time wasted. Your diagram was one of a few I crunched out back to back a few months ago, and that was a careless error on my part.

Lane

[halfspec]

And when I say "need to go back to the battery directly, using 12Awg for each of the two fan relays" you don't actually have to go all the way back to the battery with two 12AWG runs. You could easily pickup that kind of power at the starter or alternator since you should have some beefy supply wiring feeding both of those.

Lane

[ls3_rob]

Good News, Bad news

The Good News is that the og wiring you modified for me was indeed the culprit and now wired with 12v source instead of ignition using 12 gauge and 30amp fuses going to battery. It works without drawing too many amps and has yet to die/fail.

The fans kick on at 210 degrees and the ac will cycle on/off like it supposed to

The Bad News is the fans continue to run when the car is shut off. I have to put the key in the on position after shutting the car off to get the fans to stop running.  I can run a kill switch but is there any reason as to why they still run wiring them using the battery now instead of the ignition?

Thanks for all the help you do for me and the community

[halfspec]

Well shit! That's another one on me 

Take #3 (sorry its a mess with a bunch of 12V switched boxes, but I'm home alone with the kids):



While the main supply wiring that goes through the relay contacts can be straight to the battery, the topside of the relay coils (pin 86 in the diagram) need to stay on 12V switched to turn off when you pull the key. That way, even if the PCM is sending a ground out to tell the relay to stay on, the coil loses its 12V from the ignition switch, so it has no choice but to turn off.

Really sorry about the 2x mess-ups Rob. You try and help someone and make their life even harder 
I guess that's what I get for getting out of the game and thinking I can still do what I used to do.

Related topic. All LS PCMs I've encountered do what yours is doing. It's kinda like a radiator fan turbo timer. The PCM outputs the fan ground as long as your coolant temp is above the setpoint even after power is removed from the PCM. Some people like it. Most think its weird. For the folks that don't like it / think it's weird, the diagram in this post should resolve the issue.

Lane

[Cobranut]

Lane,

I was looking at the diagram, and even if the PCM output opens, there was still another path through D2 and the compressor relay coil, back to sw12v, and all the other loads attached to that. I doubt the one relay would pass enough current to pull in the fan relays, but it could slowly drain the battery.

Feeding all the relay coils with sw12v should eliminate that possibility as well.

[halfspec]

Lane,

I was looking at the diagram, and even if the PCM output opens, there was still another path through D2 and the compressor relay coil, back to sw12v, and all the other loads attached to that. I doubt the one relay would pass enough current to pull in the fan relays, but it could slowly drain the battery.

Feeding all the relay coils with sw12v should eliminate that possibility as well.

No. That section of the circuit only deals with grounds. In fact, in my diagram the bottom side of the coils / Pin 85 is the ground side of all the relays for the sake of consistency. The top side / pin 86 is the only side that reacts to 12v. Feeding 12v to any pin 85 in my diagram wouldn't do a thing, since pin 86 would already have 12v on it and you'd have 0v of potential across the coil.

Respectfully, I think you're mixed up about the operation.

There are three states where the fan relay output gets a ground.

State 1 - The PCM orders low speed output due to hot coolant temps. Notice the polarity of D2 stops the AC compressor relay from receiving a ground.



State 2 - The RPM window switch is within its 'RPM window' and hence delivers a ground to pin 30 of the AC signal relay, while concurrently, the AC button is pressed, which gives a ground to pin 85 of the AC signal relay latching 30 to 87 and allowing the ground to activate the compressor relay. Note D3 stops the PCM's low speed fan output from receiving an external ground (gets you a MIL light and a fault code).



State 3 - States 1 and 2 occur simultaneously:



States 2 and 3 are where you can run into a problem with the LS PCM sending a ground to the Fan Relay output and keeping the radiator fans on even after the PCM loses power and they stay on until the coolant temps come down below the low setpoint. Delete the whole rest of the AC circuit and the LS PCM fan outputs still behave this way.

The original LSX AC circuit posted in this thread had the benefit of being endlessly bench tested on my own FD and after that, went out to ~50 of my own customers before I posted it here. Rob's diagrams were turned out in a few minutes while my kids were probably screaming at me

Lane

[Cobranut]

I was referring to when the fan relay coils were connected to constant 12v.  The current path would be through both fan relay coils, through forward-biased D2, and the compressor relay coil back to sw12v, which when turned off would be pulled down by all the other switched loads in the car.

Supplying the relay coils with sw12v solves all the issues.