Some Details...
 

Some more photos of the circuit board, and what I am able to identify as important components.




Wires coming from the top of the terminal strip go into the circuitry of the PCB on the inside of the unit. Wires from the bottom are for external connections.

The wires connecting to terminals 5 & 6 are 120V 60Hz power for the outdoor unit. Power ground wire attaches to a terminal on the chassis (not shown). I checked for continuity between all terminals and ground and found no continuity on any terminal. I have not yet powered the system to test for voltages.



I did my best to figure out some of the circuitry.


The next two photos are connections that are NOT on the drawing. Note that these components are NOT on a circuit board and attach directly to the sheet metal frame of the heat pump.



Your comments are invited...

Best,

-AC

AC,
If the schematic i found is close to your unit, here's what the pins should be:
main cnr:
1: serial communication
2: ground
3: 17V power source
4: indoor fan motor pwm signal (varying DC?)
but all this don't matter cuz the unit works.
you can interface thru the 1-wire comms (hard) or tie into IC8 (easy) to control the unit.

Here's the schematic for the main PCB IC chip. It is a 54 pin microprocessor with the designation TMS370C08, which I looked up. I could find the PDFs for that chip, in 40 pin packages, but not in the 54 pin configuration:


An here is a photo of the main IC on the PCB. It is also a 54 pin IC. I was not able to locate any info from these numbers:


My guess is that it very well could be the same IC, with different LG branding.

So, if I'm understanding, since this PCB seems to be working OK (so far) and if it is the same chip, I should be able to control my unit by cutting the relevant chip traces, and patching an Arduino or something into the traces and sending control signals from the Arduino, right?

And if the IC on the PCB is functionally equivalent to the IC in the schematic, then the task becomes much easier.

Is there something I could measure or test that would give us a higher level of confidence of this equivalence?


By the way, I did check your assessment of pins 1, 2, 3, 4 (I assume by pins you are referring to the terminal connections)

I tested pin 2 as ground and pin 3 as 17VDC, and I get "-20.28V" so it looks like pin 3 is ground on my unit and pin 2 is DV voltage = 20.28. I checked my multimeter cables & pin numbers and readings several times and it looks reliable.

With my multimeter, I couldn't see any AC action on pin 3-to-pin-1 or from 3-to-pin-4.

I also noticed that there is a red LED on the PCB that is flashing some pattern, and that the green LED is also flashing some pattern. Maybe the unit is searching for the indoor unit? Lost baby, maybe?


Oh, I finally see what you meant by, "or tie into IC8 (easy) to control the unit.."

You mean this thing, don't you:


... and that would be this IC that happens to be sitting right next to the main controller IC...



Now I see that jeff5may is very, very clever!

Best,

-AC

So, it looks like the functions I want to control are:

• Compressor
• Heater
• Fan
• 4-Way (AKA: reversing valve)

... and that by cutting the traces that lead from IC1 pins number 27, 26, 25, and 22 and by tyeing the appropriate leads from my Arduino or whatever, to those pins, I could thereby control the heat pump, yes?

And would the functioning of IC1, to monitor for failure conditions and take appropriate shutdown actions, still function?

Best,

-AC

AC-Hacker

You may be able to wire a thermostat to the IC8. It is illustrating the relays for the 4 basic controls. You might not require the embelishment of the Arduino. For the in-floor heating a cheap programmable thermostat with its thermistor removed and mounted next to the tube in the floor would be all thats required.

Randen

I like that...

If I use it as a heating only unit, I'll want to have the heater ON during my heating season. And depending on the non-activated state of the 4-way (probably A/C mode by default), I could either permanently activate it, or leave it permanently de-activated. That would leave just the compressor & fan to control. However, I would still need to include a time-delay because since I'm bypassing the brain chip, it probably has no delay circuit.

-AC

Ok, so the mfr JUST HAD TO reverse the wires between the pc board and the terminal block. In this case, wire colors don't lie.

BLUE: indoor fan motor speed
BLACK: GND
BROWN: PWR
RED: Serial comms

If if and only if (science-babble)you and/or your people can reverse engineer serial comms with this beast, you will use the red wire. Of course, a compatible indoor unit to borrow would be of immense help. Without one, a good computer scientist could figure out what language this chip speaks and assemble a virtual indoor unit. Then the outdoor unit could remain in control of its own parts, but still integrate into your system thru the virtual interface (that you could possibly integrate into an arduino control program for serial comms?) which would control both the gshp and the ashp. And it sounds easier than it is.

Forget about the blue wire unless the above sounds doable AND you want to rig up a variable-speed pump to control your indoor water temperature.

So you're on the right track with using IC 8 to assume command of the outdoor unit. Applying voltage (from IC1 pin 20) to pins 1 to 6 will activate the brawny components on the output side of IC 8 reliably. You can do this directly or indirectly, which begs another question: Where will the arduino controller live? Will it be a replacement for the microcontroller in the ashp only, or will you want it to do more?

Like Xringer said, you may be able to get away with faking the test mode button to indirectly assume control of IC1 and all of its built-in ability. IMHO, this would be the way to go if it works. If the unit faults out after 5 minutes, just feed it another keypress train after 4:45 if you want it to keep operating. If not, let it shut down on its own. Then again, it might just run and run until you tell it to stop. It just might be the ticket: less is more. Can't hurt to try.

If you decide to directly switch IC8 to control components, you will lose all of the marvellousness built into IC1. All the "what if's" will have to be accounted for and built into your control sketch. You could do this remotely with a 1-wire addressable switch chip or directly with an arduino board. The sky's the limit.

Sounds great. Is it OK to connect directly, or should I use some kind of resistor? I can see that this would be the perfect way to deal with the 4-way, since I have no plan at this time to use the unit for cooling.

I really like randen's suggestion to put a programmable thermostat on the output (actually I plan to use an output tank, so that will be where I would attach the thermo).

I have so many projects in the air already, that I need to limit complexity as much as possible.

Yeah, this sounds great. One problem with that approach that I'm wrestling with is, assuming that the TEST KEY is a toggle (ON & OFF), then how will the system know what state the heat pump is in? I mean, if the process skips a beat, then the unit will go OFF when heat is required, and go ON when too much heat has been reached.

If I did a hardware solution, and used a temperature sensitive snap-disk switch as a run-away heat limiter, and a refrigerant pressure limiting switch, I think I'd be covered.

I don't know which one would be the least hassle in the long run.

Not for me, the sky is already filled with too many flying projects!

I think I am becoming the Samouri EcoRenovator, chop, chop...

Best,

-AC

AC Hacker

Is the reversing valve spring loaded or would it have a pilot solenoid on each end. Once the pilot valve has shuttled the spool should stay there either heating or cooling. What is your thought on the output tank? I find that the floor responds so slowly short cycle won't be your problem and the temp is so low. I would think you could plumb your floor directly from your HX.

We have a lot of good ideas for you Samouri, you should work faster, chop chop.

Randen

AC,
You can easily hotwire the unit either way.

On the one hand, if the unit will work by using the test button functionality, you shouldn't have to worry about defrost or fail-safes. Rigging up a button-press faker would be simple and cheap. When your tstat called for heat, the board would fake a few button presses, when the tstat stopped calling for heat, the board would fake a different number of button presses. The end. You'll need to verify that the unit will behave in test mode, though.

On the other hand, you would need to rig up something that would handle the what-if situations. Controlling the individual components is the easy part. Dealing with defrost, locked fan motor, locked compressor, condensor overheat, short-cycle, etc is the hard part. The tstat would only act as the "on-off" switch for your control rig. You could probably cobble up a low-tech control from parts out of a dehumidifier, but it won't act the same as something more refined.