Ultimate LSX AC Control Tutorial - HalfSpec Engineering

[halfspec]

As I step back from producing products for the RX7 community I wanted to turn over my designs and convert my projects into a more open source form. This is one of those projects.

Terms of use – I am releasing this information freely and you can do whatever you wish with it. All that I ask is that if you do post this information elsewhere, please provide a link back to this thread. As far as support goes, this thread is it. Please don’t PM me with circuit specific or troubleshooting questions. If you have questions, post here and let the very capable community here work it out. If the question can’t be answered by the community I will hop in and answer (I’m subscribed to this thread).

93-95 RX7 LSX AC Control

This is a tutorial for constructing and installing an electrical interface system that fully controls your GM compressor as a standalone unit actuated with the stock FD AC button. In its simplest form this is a universal control system that can be adapted to any engine but in this tutorial it’s really presented for 93-95 RX7 owners running a LSX engine (LS2, LS3, LS7, LS9, etc). If you have a LS1 fbody PCM and engine, this will also work for you, but you have better & cheaper options available to you here. This is the exact design I used to create and sell ~75 of these controllers over 3 years and they performed flawlessly with zero returns.

Diagram:



This diagram should look somewhat familiar as it takes ideas from Pez and burtoncr’s diagrams released years ago. The biggest differences in my design is a diode network designed to allow the PCM and the aftermarket AC controller access to the radiator fan relay(s) without interfering with each other or causing CEL codes. Additionally the design includes a more sophisticated way of handling the AC request signal from the OEM wiring. The AC Signal Intercept adapter. This is a plug-and-play adapter I developed that standardizes the controller wiring but more on that later.

Purpose for a standalone controller

The purpose for this controller is something I’ve been asked more than a few times as most people expect to be able to use the LSX PCM to control the AC similar to what the LS1 PCM is capable of. While the LSX PCM does have the built in I/O and logic to control the AC, there is one problem. The CAN bus.
On post fbody LS1 control systems the analog AC request is accepted by the BCM module then relayed to the PCM via the CAN bus. All RX7 swaps I’ve seen to date have never swapped over the BCM so with a LSX swap and the desire the add AC you’re generally starting with a missing piece.
The correct way to solve this problem would be to design a CAN bus interface that can accept an analog input from an AC request button/switch and outputs that request via a CAN bus code to the PCM. For this to work the CAN bus network to the PCM would have to be rebuilt between the PCM and this new device and then you’d have to turn off a lot of CEL codes since I expect the PCM would report a lot of hardware missing since with an active CAN network it would assume a lot of data is not being reported by the “BCM.”
I tried looking into the route above and may still design a solution down the road, but it is far more complex and undocumented.

Until then, we have another option for AC control. That option is to control the AC system with a standalone controller, which is what this is.

How it works:

This section isn’t critical to understand, but I’m going to write it out anyway because if you have problems with the controller, this section is what you’ll need to debug it.

RX7 AC Button Signal and the Micro SPST Relay:

This is usually the hardest part for people to grasp. I get questions a lot simply asking how to tap into the RX7’s AC button signal and what is it (12V or Gnd)? The button is overcomplicated in its stock form for such a simple operation. That’s one of the reasons for the AC Signal Intercept Adapter, as it cuts the complexity in half. With the interceptor installed, here’s how it all works:



In the diagram above the AC switch on the lower right. Notice that it's normally open. See the leg that exits out of 1G. That's the path to ground. How? You'll see it make its way to position 1 of the blower switch. When you switch the blower switch, this is how it gets ground.

Position #1 = Direct patch to ground through the switch
Position #2 = Path to ground through the diode then to through the switch
Position #3 = Path to ground through the diode then through the second resistor then through the switch
Position #4 - Path to ground through the diode then through the second and third resistors then through the switch
My theory on position 3 and 4 and the resistors is that the resistors are very low resistance (like 1-2ohms so they're negligible). The first resistor is a little more substantial therefore the diode path is there to shortcut it in position 2, 3, and 4.

*Note* A fully functioning blower resistor is key to getting a ground signal to the AC switch. If you have a break in the blower resistor’s wiring, your AC won’t function in 1 or more positions. This is important because I’ve seen this problem with customers several times over the years and it appears to be getting more and more common as our cars are getting into their mid 20s. If your AC button doesn’t actuate the mini SPST relay, my first suggestion is to inspect and verify your blower resistor is working.

When you press the AC switch and your blower switch is in position 1-4 you get a ground out of 1l. This makes its way to the thermoswitch connection G-08.

This is where my proposed adapter picks up the signal. Creating an adapter at G-08 to pickup the signal after the thermoswitch allows us to pick up that ground coming from 1l and use it to activate the Micro SPST relay. Pay special attention to how the AC Signal Intercept Adapter is wired. The violet wire does not pass through to the other side of the adapter. It gets re-routed directly to the micro relay pin 85. You have to do it this way to insure that the factory Fan #1 relay doesn’t interfere with the AC request signal.

When the ground signal from the RX7 AC switch activates the Micro SPST relay we short the path between pins 87 and 30 which allows the RPM Window Switch’s white output to connect to the AC Pressure Switch.

RPM Window Switch:

The Baker Electronix RWSr Window switch performs 1 step of the control logic to turn on the AC compressor. Its job is simply to determine if the engine RPM is running between 400 and 4800 RPM. If the engine RPM falls out of this range the White output wire is simply Open and if passed through the Micro SPST relay AND the AC Pressure Switch will NOT activate the Mini SPST relay nor provide a Ground at the Fan Relay Output. Only when the engine’s RPM range IS between 400-4800 RPM will the white output issue a Ground signal, which if passed through the Micro SPST relay AND the AC Pressure switch WILL activate the Mini SPST relay AND provide a Ground at the Fan Relay Output.

AC Pressure Switch

This is a binary switch with ~13psi of hysteresis and the last step of the control logic. Its primary function is to ONLY pass the Ground command to start the compressor IF the refrigerant pressure is within range. My sensor of choice, the Ryder 1514, levels are as follows: High: Off: 455 On: 341. Low: Off: 28 On: 40. Essentially that means your refrigerant pressure needs to be between 40 and 341 PSI for the AC switch to pass the Ground generated by the RPM window switch and being passed through the Micro SPST relay.

Mini SPST Relay:

Once the RPM window switch generates a Ground and it passes through the Micro SPST relay (actuated by the stock AC Switch), and finally passes the AC switch it arrives at Diode #2 (read below) and the Mini SPST relay contact # 85. The Ground on 85 activates the relay and 12V is sent to actuate the AC Compressor clutch which, if your evaporator, expansion valve, condenser, radiator fans, cabin fan, and air routing within the heater box is working means cold air in yo face!

Those Damned Diodes & Fan Control:

Diode 1 is called a flyback diode and it’s a type of snubber circuit. It’s actually built into the LSX harness wiring for the compressor if you’ve actually pulled one apart. When the voltage to the compressor clutch solenoid is removed the coil’s magnetic field collapses which creates a pulse of current flow which therefore creates a negative voltage across the solenoid coil. This short lived reverse voltage is only around in the order of miliseconds, but it can be a couple hundred volts…. Which can pop the mini relay to the left.  The flyback diode (it’s just a regular 1N4004 diode) can snub this reverse voltage because when it pops up, it forward biases the diode which sinks everything to ground therefore protecting your relay.

Diode 2 and 3 work together to provide a Ground fan output signal for your fan control relay, but they are arranged in such a way that neither side of the control gets feedback from each other.

Diode 2 will bias when the AC pressure switch passes a Ground, therefore the Fan Relay Output will see Ground. Simultaneously, when Diode 2 is passing a Ground Diode 3 blocks it as a Ground condition on the PCM fan output (that it didn’t command) produces a CEL code.

Diode 3 will bias when the PCM ouput passes a Ground (the PCM will output as normal when coolant temp rises above a setpoint) therefore the Fan Relay Output will see Ground. Simultaneously, when Diode 3 is passing a Ground, Diode 2 blocks it as a Ground condition that sees the Mini Relay contact 85 would trigger the relay and activate the AC Compressor Clutch which you wouldn’t want as every time your radiator fans come on to cool your coolant levels the AC compressor would come on too).


- Lane

[halfspec]

Parts List



*Note* Pay special attention to the orange and yellow highlighting concerning your compressor connector choice. Different engines use different compressors and this will trip you up in more ways than one. The first hurdle relates to the compressor clutch connection. LS3 SS Camaro's use LS1 style connectors so I've included the part numbers to build that connector. CTSV LS3's use a different compressor that has a less standard connector that I haven't been able to figure out how to build from scratch. Luckily you can buy the connector pre-assembled but it's expensive by comparison. If you have a compressor that uses a connector other than these two you'll have to do some digging.

The parts list above is fairly comprehensive. The only thing you may run into is order quantity limitations. Waytekwire is especially picky about low quantity orders which is why I tried to add as many alternatives as possible. Either way, this should give anyone a huge head start on getting one of these high quality controllers built even if the original sources dry up.

Tools of the Trade

As with everything car related, you have to have the right tools to do the job well. That is especially true when you're building something like this. A high quality stripper / crimper will make your life a lot easier, whereas the incorrectly spec'd or insufficient stripper / crimper will make your life a living hell. Believe me. This will be one of the big hurdles DIY folks will face, because we're not just talking pocket change here.

I own the following 3 crimpers:

Pressmaster KRB-0560


S & G Tool Aid 18920


Cycle Terminal ECT47


I also own the following stripper:

IDEAL 45-092 Stripmaster Wire Stripper


All 4 of the tools above have been worth their weight in gold.

The S & G Tool Aid 18920 was my first ratcheting crimper. It's a good starter crimper and does a lot of things pretty well in the medium of its range. It can handle Delphi 150-480 terminals and it has a great die for crimping barrels & butts.  It's the large and small stuff where it starts to struggle (see my comments on the next two crimpers). I believe a good alternative for this crimper is the Cycle Terminal Eclipse Crimper. The only thing I'm not sure about when it comes to the Eclipse crimper is what dies it comes with and what you have to purchase seperately. It makes it sound like it comes with the barrel / bullet die already which would mean you'd probably want the optional "Die for Open Barrel Terminals" or "Die for Small Ring and Splice Terminals " depending on what you're crimping. May be a way to save money over the S&G depending on your application.

The Cycle Terminal ECT47 crimper is for small stuff. I use it almost exclusively for crimping PCM terminals as they're generally made for 20-24AWG wiring and it's just too small for the ratcheting crimpers I have.

The Pressmaster is absolutely amazing. I bought it late in the game as I resisted paying $150+ for a crimper for years. However, after getting it I can't believe how much time and pain it saves me. This is the only crimper I own that can crimp the .312 YMST1418L / YFST1416N terminals. The S&G just doesn't have the leverage to do bigger terminals unless you're related to Hercules and/or can figure out how to use your hydraulic press to help actuate the handles. Seriously, I kiss this one every night before I go to bed.

The ideal stripmaster is one of those tools you can't believe you lived without before you got it. Seriously, it's saved me DAYS in time over the years I've owned it.

Finally, when doing work with small terminals and connection systems that use tangs / locking tabs to secure the terminals, it is VERY important that you have the proper tools to de-pin the connector you're working on. Seriously, you can do a lot of damage and waste a lot of your time trying to use a tool that isn't designed to de-pin. I suggest getting the $13 option from cycle terminal that includes a wide and narrow de-pinning tool:



Lane

[halfspec]

Build Instructions

I imagine this is the section most folks are waiting for 

Step 1 - Build the Power Harness




The specifics parts needed are:

6ft Pink 14AWG TXL/GXL wire (main length section)
2in Pink 14AWG TXL/GXL wire (fish-hook / fuse box connection section)
Two lengths of 2 1/2in Pink 18AWG TXL/GXL wire
Mini in-line fuse holder - 46025
Mini 25 A fuse - 46258
.312 Male Terminal = YMST1418L
.312 Female Terminal = YFST1416N
Mini relay terminal = 75280
Micro relay terminal = 75290



1. On the first end, solder and shrink wrap the 14AWG wire and the fuse holder.
2. On the other end of the fuse holder slice a section exposing bare wire and solder one of the 18AWG wires to it. *Note* Plan and shrinkwrap this connection.
3. At the end of the fuse holder wiring, crimp the Mini relay terminal together with a 2 1/2" Pink 18AWG wire.
4. At the end of the 2 1/2" Pink 18 AWG wire, crimp a micro relay terminal along with the second length of 2 1/2" Pink 18AWG wire


1. On the second end of the 14AWG pink wire, crimp the .312 Male Terminal together with the 2 1/2" pink 14AWG wire.
2. On the other end of the 2 1/2" pink 14AWG wire crimp the female .312 Female Terminal

Step 2 - Build the Pressure Sensor + Fan Control Harness




The specifics parts needed are:

6ft Purple 18AWG TXL/GXL wire
6ft Gray 18AWG TXL/GXL wire
18in Black 18AWG TXL/GXL wire
18in Orange/Black 18AWG TXL/GXL wire
2in Black 18AWG TXL/GXL wire
2in Pink 14AWG TXL/GXL wire (fish-hook / fuse box connection section)
Two lengths of 2 1/2in Pink 18AWG TXL/GXL wire
Two Pressure Sensor Terminals   829-12084200
Pressure Sensor Connector   829-12052641
Pressure Sensor Lock   829-12052634
AC Pressure Sensor Connector Seal   829-15324818
Two Mini relay terminal = 75280
Two Diodes - 512-1N4004




1. Slide the seals onto the gray and purple wires
2. Crimp the terminals on the end of the gray and purple wires.
3. Push the terminals into the pressure sensor connector as well as the seals until the seat and click
4. Install the secondary lock (blue piece)
5. Sleeve if so desired

On the other end of the gray and purple wires:



1. Arrange and solder the diodes, black, and orange/black wires together as shown



1. Plan and heatshrink the exposed diode leads then install one more piece of heatshrink to cover the rest of the diodes (not shown)
2. Crimp a Mini relay terminal together with the purple and black wire.
3. Crimp a Mini relay terminal  on the gray wire.

Step 3 - Build the Compressor Clutch harness




*Note this tutorial only shows how to build the harness tipped with a connector suitable for a SS LS3 camaro compressor. If you have a CTSV LS3 compressor or other, you'll need a different connector.

The specifics parts needed are:

8ft Black 16AWG TXL/GXL wire
8ft Dark Green 16WG TXL/GXL wire
Two AC Compressor Terminals - 829-12048074
AC Compressor Connector - 829-12162017-B
AC Compressor Connector Lock - 829-12124824-B
Two AC Compressor Connector Seals - 829-15324973
Mini relay terminal -75280
One Diode - 512-1N4004



1. Slide the seals on the dark green and black wires.
2. Position the diode so the legs slide through each of the seals and meet the tips of the black and green wire. Note the polarity orientation in the pic and schematic! Note 2 - Involving the the diode makes this a tricky crimping operation. I'd recommend dabbing the crimping section of each terminal with solder if possible to insure the diode is bonded to the terminals.
3. Crimp the terminals on the dark green and black wires.




1. Align and press in the terminals and seals in the compressor connector.
2. Sleeve if so desired



1. Crimp the Mini relay terminal on the end of the dark green wire.

Step 4 - Build the AC Signal Intercept Adapter



The specifics parts needed are:

3ft Purple 18AWG TXL/GXL wire
3 sections of 2 1/2in gray 16WG TXL/GXL wire
Micro relay terminal -75290
Yazaki CN-A 4 pin Connector Set




1. Crimp a Yazaki CN-A male and female terminal on each of the 3 sections of 2 1/2in gray 16WG TXL/GXL wire
2. Crimp the Micro relay terminal on one of the 3ft Purple 18AWG TXL/GXL wire
3. Crimp a Yazaki CN-A female on the other end of the 3ft Purple 18AWG TXL/GXL wire
4. Assemble exactly as shown.

Step 5 - Window Switch Installation + Final Assembly




The specifics parts needed are:

Ground Terminal Ring -31004
Mini relay terminal - 75280
Micro relay terminal - 75290

1. Using the main LSX circuit above land all the harnesses you built previously to the mini and micro relay sockets.
2. Install the RPM window switch
    a. Crimp the Mini relay terminal on the end of the RPM switch's green wire and connect it to the micro relay pin 30
    b. Crimp the Micro relay terminal to both the RPM window switch's red wire AND the loose pink end off your Power harness you build earlier. Connect it to the micro relay pin 86
    c. Crimp the Ground Terminal Ring to both the RPM window switch's black wire AND the loose black wire off your Compressor harness you built earlier.
3. Install relays
4. Have a beer or 10.

Closing Notes

1. You may notice that I sometimes say connect to pin 85 in my schematics and I connect to pin 86 in my pictures or vice versa. Polarity doesn't matter with the relays I've specified so the two are 
    interchangeable. As long as a ground is on one side and 12V is on the other side, the relay will activate. Pins 87 and 30 are also interchangeable. I just make use of this fact to simplify wiring.
2. If you want to get into the nitty gritty. I don't crimp my seals correctly in the pictures above. The secondary crimp on the terminals is supposed to be used to crimp the seal AND the wire insulation like this:

As a amateur I just crimped to the wire insulation as having the seals movable have me a little bit of flex for moving things around like the diode on the compressor connector. Still, if seals are involved, and you want to do it right, try and do it like the picture above shows.

- Lane

[halfspec]

Installation

Ok so you’ve got your controller built and it looks a little something like this:




Time to install it!

This installation tutorial is divided up into 3 parts. Part 1 covers the RX7 electronics side of the install. Part 2 covers optional connections. Part 3 covers the initial power up and testing.

Part 1 – RX7 and chassis wiring



1.   This controller is made to be mounted in the passenger side kickpanel area, so that’s where it will be easiest to locate everything unless you’ve tailored your wiring and deviated from the plans above.
2.   Prepare 1 of the 3 or 4 studs in that area to be used as a ground location. This means to remove any paint down to the bare metal and any dirt away from the base of the stud.
3.   Using the 6mm lock nut included in your kit, bolt the ground terminal to this prepared stud. See the pic below:


Note – This stud has NOT been prepared properly. Please make sure the ground terminal makes good contact with bare metal at the base of the stud.

4.   Remove the 25A fuse from the 12V switched wire.
5.   After removing the fuse, route the 12V Switched plug from the passenger side to the driver’s kick panel. I find that routing along the firewall and over the transmission tunnel to be the most direct / clean route.
6.   Unplug, unbolt, and unclip the driver’s side fuse box. Tip #1 – Remove your kick panel and dead pedal. Tip #2 the fuse box has one bolt towards the floor board and one VERY hard to reach clip at the top (See pic below). Please be careful not to break this clip. It is possible to see the clip with some finagling, but it IS difficult and probably one of the more frustrating parts of the job.



7.   Flip the fuse box over and look for 3 position black connector with three large wires colored Blue, Black/White, and Black/Yellow.



8.   Unplug the black connector and use a small flat head screw driver to de-pin the Black/Yellow wire.



9.   The pin should come out looking like this:



10.   Slide some ¼” shrink up and over the female terminal above.
11.   Install the Male side of the 12V Switched Plug onto the original Female terminal above, then heat the shrink-wrap over the connection (not shown).
12.   Plug the Female side of the 12V switched Plug into the black connector like this:



13.   Push the connector into the black connector until it clicks.
14.   Reassemble your fuse box and replace any panels you removed to access it.
15.   From the passenger kick panel, plug the A/C G-08 Signal intercept adapter between the Evaporator’s Dash Wiring and its Thermoswitch:

*Note* G-08’s location has been a subject of confusion for many over the years I sold this controller. Folks can’t seem to find the thermoswitch plug G-08. It’s slightly different for Mana and Denso evaporators. Here is the diagramed location:


The thermoswitch is labeled as '4' in the pictures above and G-08 is the 4 pin electrical connector at the end of its wiring pigtail

Here’s my Denso connector hanging down from its clip (It’ll be clipped up further in the dash via its stock configuration unless someone’s been toying around (like me in this picture))



And finally, here’s a member’s Mana G-08 clipped to the evaporator case as it should be:



16.     Take the green RPM wire and tap into the RPM signal coming from your PCM and leading to your Tachometer. It is reccomended that this connection be soldered and heatshrinked or crimped and heatshrinked.
17.   From the passenger kick panel, route the compressor control plug to the compressor. The length instructions above are meant to route through the airbag harness grommet and up and over the inside of the fender to right in front of the wheel where it can easily make its way to the compressor. Kind of like the picture above but on the passenger side:



18.   The method above does require the temporary removal of your fender.
19.   Another method would be to route through the engine harness grommet or drill a new hole and install a new grommet to pass through.
20.   Plug in the compressor control plug.

Optional Connections

1.   This design includes the ability to provide a GROUND to a fan relay coil when the A/C switch is pressed as well as provide a path for PCM control of that fan without interfering with the PCM. The idea being that the fan will provide additional cooling for the condenser when the car has the A/C running in stop and go traffic.
2.   Most fan setups involve the PCM to provide primary control of the fans.
3.   In the setup mentioned in the above step the PCM has two wires that lead to 2 or 3 relays to control high and low speeds.
4.   The PCM grounds the low speed wire to enable low speed operation and also grounds the high speed wire to enable high speed operation.
5.   The way the fan function works in my kit is that it passes commands from the PCM through its wiring, but also has the ability to override these commands and turn the fan on by itself when the A/C button is installed.
6.   To install this feature:
   a.   Severe / Cut the low speed wire connection between the PCM and the Low speed relay.
   b.   Splice the A/C Controller’s Orange with Black strip wire to the wire leading back to the PCM. It is recommended that this connection be soldered and heatshrinked or butt crimped and heatshrinked.
   c.   Splice the A/C Controller’s Black wire to the wire leading out to the low speed fan relay. It is recommended that this connection be soldered and heatshrinked or butt crimped and heatshrinked.


Part 3 – Powering up and testing

1.   Plug the 25A fuse into the 12V Switched wire’s fuse holder which is near the relays in the passenger kick panel area.
2.   If your system isn’t charged and your pressure switch isn’t installed, you’ll have to jump the pressure switch connector with something line a non-insulated (bare metal) paper clip. The pressure switch used with the LS2/LS3 kit is simply a on off switch and has no polarity. It stays closed when the pressure is right in the system and passes the signal through it. It opens up when the pressure is too low or too high and breaks the signal passing through it.
So, to test without actually having the system charged up and the pressure switch installed, you have to jump the two terminals on the pressure switch connector with something like a paper clip.
3.   Turn your key to the ON position (don’t start the car yet).
4.   Check the RPM switch to see that its indicator LED turns solid blue then starts to pulse blue.
5.   Crank your car and verify that the RPM switch’s main indicator LED turns slightly purple. This indicates that the switch is accepting the RPM signal from the PCM and adds some red light to the indicator LED which signals that the switch is allowing the AC to be turned on (IE the car’s RPM is within a safe range). If you turn off the engine or rev over 4800 rpm you will see the the main LED turn back to solid blue (indicating that the RPMs are too low or too high for the AC compressor to be on).


RPM switch with purple indicator light (car on and idling)

6.    With the car still on, turn on your A/C blower motor, then press the A/C button. You should hear at least one of the relay’s click or at least feel it click if you touch it while toggling the A/C switch. You can also check the compressor clutch connector with a voltmeter (if you happen to have one) and you’ll see 12v. Additionally, if you have hooked up the fan control wires, you should hear and see your fans turn on. If it does you’re done with the exception that you may need to reconnect your compressor plug and pressure sensor plug if you unplugged them for testing.
If not, check the unit’s 25A fuse. If the fuse is intact, check your ground terminal. If needed, clean the contact point again. If that fails, move the ground to another location. If it still doesn’t click when pressing the A/C switch please post your questions here and the norotors member will help you.

Otherwise, you should now be able to enjoy the full benefits of having a safely controlled A/C system.

- Lane

[markfluko]

Phew, almost commented right before you made those reservations 

Badass work man, real easy to follow.

[halfspec]

Phew, almost commented right before you made those reservations 

Badass work man, real easy to follow.

Whoah! Almost ninja'd my ninja edit 
Glad you're enjoying it so far. Much more to come.

Lane

[halfspec]

Done



Lane

[ccadkins1]

Hello Lane,
I'm apparently the world's biggest idiot, because I'm having trouble getting my AC working.  Hope you can help me!

Some time ago, I bought a line set, dryer, etc. from you, as well as the window switch setup for standalone control.  My swap involves an '04 GTO engine and harness, therefore a lot of the nice ac/fan control isn't present in my PCM.

I have everything installed in the car (lines, dryer, harnesses, etc.).  My GTO PCM controls my main cooling fan, and I have a secondary fan installed for aux. cooling when the AC is on.  Where do I tap into in order to pull a relay to gnd and activate my secondary fan?  Should I just tie into the compressor control plug? (I doubt that's the answer!)

Any help is appreciated!

Chris Adkins

[halfspec]

Hey Chris

Your answer is in your original installation tutorial or post 3 above. Specifically:

Optional Connections

1.   This design includes the ability to provide a GROUND to a fan relay coil when the A/C switch is pressed as well as provide a path for PCM control of that fan without interfering with the PCM. The idea being that the fan will provide additional cooling for the condenser when the car has the A/C running in stop and go traffic.
2.   Most fan setups involve the PCM to provide primary control of the fans.
3.   In the setup mentioned in the above step the PCM has two wires that lead to 2 or 3 relays to control high and low speeds.
4.   The PCM grounds the low speed wire to enable low speed operation and also grounds the high speed wire to enable high speed operation.
5.   The way the fan function works in my kit is that it passes commands from the PCM through its wiring, but also has the ability to override these commands and turn the fan on by itself when the A/C button is installed.
6.   To install this feature:
   a.   Severe / Cut the low speed wire connection between the PCM and the Low speed relay.
   b.   Splice the A/C Controller’s Orange with Black strip wire to the wire leading back to the PCM. It is recommended that this connection be soldered and heatshrinked or butt crimped and heatshrinked.
   c.   Splice the A/C Controller’s Black wire to the wire leading out to the low speed fan relay. It is recommended that this connection be soldered and heatshrinked or butt crimped and heatshrinked.

In other words, you have a pair of wires coming out of the LSX AC controller. One Black and one that's Orange/Black. The Black wire is what you'd use to ground the coil of your aux fan relay. The logic for when it grounds is as follows:

Black = Ground IF AC Compressor = ON OR Orange/Black = Ground.

So your aux fan relay will come on when you press your AC button as long as the black wire is connected to your aux fan relay coil (and the other side of the coil is connected to 12v of course). The orange/black wire doesn't even have to be connected, it's just a wire that's available for your PCM in case you want to also tell the aux fan to come on when your coolant temps rise above the PCM's coolant sensor setpoint. If it's connected the PCM can also ground the black wire which can ground the aux relay coil WITHOUT the AC even being on. My schematic and wiring simply allows BOTH the AC system and the PCM access to the aux relay without interfering with each other.

Hope that answers your question.

Lane

 

[Mysta Joe]

Hey Lane, just a quick question. Does it have to be a micro and mini relay or can it be two micro?

Just sometimes in Cayman stuff isn't always available and paying shipping and duty on the items will cost me 2-3 times more than initial cost.

[halfspec]

Hey Lane, just a quick question. Does it have to be a micro and mini relay or can it be two micro?

Just sometimes in Cayman stuff isn't always available and paying shipping and duty on the items will cost me 2-3 times more than initial cost.

Maybe

I may be able to handle the load. It may not. Most GM diagrams I've seen fuse the AC compressor clutch for 15-20Amps. That's a tough continuous load like a fuel pump and not something like a defroster or pop-up headlights that use a good bit of current but are only used for minutes at a time. In my experience, micros can handle 25A just fine... for a while. Higher continuous loads seem to burn them out over time simply because they're small and their inability to dissipate heat breaks them down over time.

So I'll circle back to maybe. Maybe is usually something electrical engineers avoid when designing electronics. We'd much rather use a component that will definitely do the job and will do it well indefinitely. A mini relay can definitely do the job in this application, whereas a micro is a toss up.

I can understand the struggle being in a remote location. One suggestion would be to simply use whatever 12V relay you can find locally that's rated for 30/40 amps. The only reason I use the relays I do is because I have pretty sockets that link them together and look nice. The design doesn't require a particular type of relay as long as it's rated for the load and the coil is a 12v coil. The only thing you'd lose is a little loss in the looks department.

Lane

[ccadkins1]

Lane,
THANK YOU, THANK YOU, THANK YOU, THANK YOU, THANK YOU, THANK YOU, THANK YOU, THANK YOU, THANK YOU, THANK YOU!!!

[Mysta Joe]

Thanks for the reply and suggestion 

[dtsan]

You are my hero! Had to revive from the dead just to say that.

[halfspec]

You are my hero! Had to revive from the dead just to say that.

Glad to be of service.

Lane