Controlling a DC inverter machine
 

As I have just been given a Daikin split system which has a DC compressor I started thinking about how to control it.

The threads I have read have all focussed on using controllers from various devices and adapting them. This involves 'junking' the existing control system and starting from scratch building a DC motor controller. Has anyone succeeded in doing this?

I still don't know if the units I have actually function, that's still to test, but assuning they do I'm firstly going to try a different approach.

What would be wrong with gutting the internal unit and then using it in abox to control the external unit? The unit I have has 1 thermal sensor and the remote that signalls to the unit what to do. Why re-invent the wheel as far as the external unit is concerned?

So my plan is:
1. Get the unit working with the existing internal unit control board removed from the internal unit.
2. 'Crack' the control code - unless it is detailled in the service manual (that I'm hoping to get hold of). It signalls down 1 wire (certainly referenced to ground or neutral so I should be able to monitor it).
3. Build my own controller to manage the external unit.

Any thoughts/suggestions?

Nigel

I don´t know Daikin, I have mitsubitshi here in my house, but certainlly maybe the same. The comunication between the indoor and outdoor units it´s Serial. If you post the model of the Daikin you have we can look to find the service manual on the net it´s not diffcult.

Basically the Inverter can divide on several blocks:

-Power Filter and Rectifier
-PWM controller (compresor and fan)
-Logical and signal handling (uProcessor)

In my opinion it´s easy to try to get the unit working removing original electronics, and installing custom controller.

The models are:
External unit RXS71E3V1B
Internal unit FTX71EV1B

Compressor is 2YC63BXD

Diakin's units are some of the best on the market IMHO. They have a better reputation for reliability and their performance beats the Mitsubishi. The Fujitsu's are a little behind in reliability, it seems, but have very high efficiency in their RLS line of their Halcyon inverters. Diakin's are hard to get outside of internal HVAC distributors as they don't like the DIY community touching them.

With that aside, you are likely going to lose some efficiency by setting up your own control scheme and even moreso by building your own controller. They use a BLDC controller and if you really want to, there are people who have messed with this sort of thing on endless-sphere or you could get a BLDC controller from hobbyking but you might have a hard time getting one that won't kill itself or your compressor unless you know what you are doing.

If you want to modify the compressor control, your best bet might be letting the Diakin stock controls do their thing but trick their thermistors and other sensors to get it to do what you want.

Is there something wrong with the Diakin unit you received? Is it broken or missing control parts? I'm just trying to figure out your intent and what sort of control you are looking for since you didn't say it in your original post.

T-Run ??
 

There is a way to test a Sanyo CH2472 ODU. It's the T-Run jumper header.
I wonder if other brands have a way of running ODUs without the IDU connected.

http://i46.photobucket.com/albums/f1...r/NCL/z083.jpg
(Note: T-Run/Test connector is in the center bottom of PCB).

I'm not sure if the T-Run maintenance switch would allow the unit to run
with all it's normal functionality, like defrost etc.

Here's some videos of T-Run operation.
NCL :: Sanyo chill mode test video by Xringer - Photobucket

Green slot :: R410A cleaning loop video by Xringer - Photobucket

As far as I'm aware the machine works. It was unmounted, covered in cobwebs and in a garage and I know nothing of its history.The present owner of the house inherited it. The previous owner (who I knew) was a bit of a hoarder of junk 'just in case...'. It's missing the remote control. I'm planning to connect it up to check it out before I go too far though.

I'm not planning to replace the BLDC circuit - why bother when it (I hope) works. More a case of 'hacking' the internal units control circuit to get the external unit to do what I want. Initially using the existing control which will, I hope, enable me to decode the serial data stream. Then build my own 'indoor unit' controller using a PIC or similar (maybe a Raspberry PI - now there's an idea, I have one on order....)

As and when I get it going then maybe I'll replace my Mitsubishi that is running the heating to the house as this unit has a higher capacity (the Mitsubishi is around 6Kw ish and a conventional compressor), or maybe not.. the fun is in getting it to work.

Nigel

I once read a thread on the web about controlling Mini-splits.. Can't find it now.
But, I did find something you might want to check out..
Minisplit Inverter communication standard

Acuario,

As far as I'm concerned, this project you have going is the holy grail of heat pump hacking.

Modern mini-splits have wonderful efficiency, rivaling GSHP of a decade ago, and getting an inverter mini-split to heat water for radiant heating is such a great fit. The only existing unit that does this is the Daikin Altherma and it is really expensive.

Additionally, from my point of view, breaking the code on the inverter compressors makes them candidates for ultra high efficiency GSHPs, which would place our hacker community right at the cutting edge of the technology.

I did look at Xringer's link below and it is an absolute treasure horde of great information.

I am in touch with some pretty high-powered electronics geeks here in my home town, so if you hit a dead end, there is abundant help available.

I really like what you are doing, attempting to get the maximum effect while leaving as much of the existing developed circuitry in place.

Lots of photos and detailed descriptions will help you get more help... and ultimately help others in their projects.

Good luck on this one!

-AC_Hacker

I'm making a bit of progress - here are some pictures to keep you interested...
The comms is based on RS232, runs at 1204 baud and is 8 bits, 2 stop bits, odd parity, LSB first, non inverted.

It uses a single signalling wire from a (I guess) custom device that superimposes the signal onto the mains supply - it looks like it has a transformer encapsulated in it. I'm not too concerned with it at the moment as I'm monitoring from the low voltage side.

There are 3 signals plus power to the device. One appears to be a clock signal, one connects directly to the cpu, one is coupled via a pullup resistor to the cpu - presumably data in/out.

In idle the internal unit senda frames of data, 3 per second; the external sends 3 frames as well. Each frame is different but the frames repeat every second.

I'm trying to analyse the frames to work out what they contain; so far it looks like a unit id or address (it does change) (2 bytes) a zero byte, 16 bytes of data then a checksum byte.

The interesting bit will be working out what the 16 bytes are!

I have borrowed a remote control so at least I can get the unit to do things :-)

Nigel

Not 1200 baud?
 

IIRC, in the posts I saw (many moons ago), the hacker set up a similar kind of data stream capture,
and then used the remote to change the temperature, one degree up or down.

That allowed him to find the location of the temperature bits/commands in the stream.
I think he did the same thing for finding the 'mode' command byte(s?)
and decoded the function of each bit.
Which bit equals Fan only, Heat or Cool etc.?. Seems like a lot of work.

I've surfed the web over an hour, trying to find info on the CadillacKid (aka) Christopher in Columbus Ohio.
I'll bet he has a bunch of data we would be interested in seeing..

Maybe he will Google up this page and come join the struggle. :)

Did you contact Paul Voyland? I gave him a ring myself the other day and he hasn't gotten back to me yet. He must be busy.

Ok, probably 1200 baud - my logic probe has an auto baud function and it reported 1204; near enough.

I'm using the trace and compare brute force thing to work out what's going on - must be 20 years since I last did that! Anyway, as time permits I will keep hacking..

Nigel

Keep up the good work Nigel. I'm pretty sure the early work that I saw on the web
didn't include a clear description of the command &or status bytes &or bits.
(I may have even posted a link somewhere here, but lost track of it).

I'm hoping that you will include this kind of detailed information in your posts.
It might be a first for the WWW, :) to have this kind of industry inside data exposed.

Hopefully, the protocol and bit definitions will be standard across many product lines.
But, even if they aren't, your methods and results will still be very useful as a guide for other experimenters.

I've made some pretty significant progress since my last post - shut in my shed for the last 2 days with a pc/logic analyser/oscilloscope etc...

I can nowcommunicate with the machine and turn it on and off from my pc - no mean feat I can assure you!

It's meant a bit of electronics to interface from the PC to the internal unit control board, to be more precise - a MAX232 to interface the TTL data signal from the board to the RS232 for the serial port. I suffered big problems with interference using the MAX232 to level convert from the RS232 to the board (logic analyser/scope found the problem) so I ended up using an MC1489 line receiver - that sorted the problem. Just as well I have all the bits from when I used to design hardware.

A fair amount of programming to decode/encode/log etc. All in Visual basic at the moment.

A bit of playing with the timing sending the data frames, some head scratching over why what I was sending seemed to be ignored (it was the sequence I was using to reset the data comms) and hey presto - it functions!

There are still a lot of bytes that I don't know what they are/do but I have emulated enough using hard coded frames to be able to keep the communication going with the exernal unit (if the comms does not keep running and the machine loses the data link it shuts off - a safety feature I guess).

I know how to change the mode between heat/cool, set the temperature, monitor the temperature of the external unit thermistors and a few more things too..

It's certainly a bigger challenge than just switching on/off the compressor!

Not really anything of interest to post in terms of photos at the moment unless you enjoy the sight of a breadboard and spaghetti junction!

Will keep you informed of further progress.

Here is a snippet of what I have been working with - the data is from the machine, the labels for the frames are mine (from brute force analysing!)

F00F010680000000000000000000000000000086 Reset1
F08F000600000000000000000000000000000085 INT_RESET_1B
000F00010203150000000000000000000000002A Reset2
008F0001024704500A313E334102380000000054 INT_RESET_2
010F00010203150000000000000000000000002B Reset3
018F0001024704500A313E334102380000000055 INT_RESET_3
F80F00A2003C476A017F807F80000012000000A7 Reset4
F88F009F803A484DDD0000120000000000000064 INT_RESET_4
C10F00001880162E2E1D000000000000000000F7 ExtTempReport
D08F000102001E00000080000000001C60666042 Internal control
C20F0000002701000000000000000000000000F9 EXT_REQ_COM
C18F00001700170117811780178080000088004D INT_TEMP
D10F000000001A02020000B0B00000000010006E PostRun
D08F000102001E00000080000000001C60666042 Internal control
0F0F000102031500000000000000000000000039 Reset8
408F00E10F0000000000000000000000000000BF INT_RESET_8
C10F00001880162E2E1D000000000000000000F7 ExtTempReport
C08F000F000000770000000000000000000000D5 INT_RESTART_COMM
C20F000000780000000000000000000000000049 EXT_REQ_COM
D08F000102001E00000080000000001C60666042 Internal control

From what I have deduced the frame starts with a command byte, the frames with 0F are from the external unit, those with 8F are from the internal unit, the third byte is always 00. The final byte is the checksum for the frame. What is in the middle is the fun bit!

Nigel

Hi Nigel, great Job!!!!! this is very promising. I only worried with the logic of the PCB that controls the Outdoor unit, for example you can send a command to put the unit on in the heat mode but imagine you would like a temp on the HX of 55ºC maybe the unit don´t respond to its command due to the conditions ex Outside temp, or the safety features can be activated by the PCB preventing the target temp etc.....


But keep on the good work

Xotet

Wow, is that 20 eight bit bytes?? Somehow, I never figured it a control segment would be that long!
Don't you wish that you had a programmers manual.. ;)

Now you are getting me interested in what's coming out of the IR remote control..
Kinda wonder how long those IR bursts are.?.

A programmers manual would have been great but much less fun!

Remote control data frames aren't too long if I remember correctly. One of my first ever hacks when I was in my mid teens was an Amstrad remote control that operated a stereo (the stereo had been smashed up). It used an 8048 processor to process the commands and operate the setreo - channel change etc. I hacked the code and programmed my own 8748 device to use as a remote control to operate relays to change the channels on my TV (it was the old push button type that you had to physically change channels on).. oh the memories come flooding back.

As stated in the post you directed me to earlier, the problem is there is no feedback to the remote so you don't know what the external unit is doing.

Nigel

There are 2 frames that report the relevant temperatures the units are seeing, one from the external machine that looks like it reports 4 temperatures, one being the sensor close to the evaporator, the other 3 I guess are inside but I haven't opend it up to identify which is which yet - a bit of freezer spray quickly identifies it.

The frame from the internal unit reports the ambient temperature as seen by the sensor on the control board and the temperature of the pipe thermistor connected to the hx. So I'm guessing for now that the unit is intelligent enough to start reducing it's compressor when the temperature approaches the set temperature.

The command frame (Internal control on the dump) is where the operating mode, control to switch on/off and desired temperature is set.

Nigel

Do you have a schematic for your interface board?

I'd like to see if I can make some sense out of my Sanyo.

Thanks,

-AC

This thread rocks. You guys are awesome.

I don't know why controlling mini splits is so difficult. Even using an IR blaster appears to be an issue. If they could simply make these things interface with a normal thermostat I'd be on the bandwagon tomorrow. As it is I wouldn't be able to control them with my home automation system so I couldn't tell the AC to shut off if a door were opened for a certain amount of time or something like that.

I guess people have been recording and playing back IR data bursts for some time.

ZipLabel.Com | Computerized Infrared Remote | Introduction

Ken Shirriff's blog: An Arduino universal remote: record and playback IR signals

It seems like a home automation system based on a PC that was on 24/7,
could be set up to replace a mini-split IR controller.

If you dig a little deeper you'll find that it's not so simple. I have a system that's on 24x7 and there are enormous obstacles in controlling a mini split. There is a form of handshake between the remote and the head unit.

There is feedback. When the room temperature changes,
the remote sends out a data stream to tell the system to take a break, or work harder.. :)

But, my understanding of the Sanyo remote, the data flow is one-way.
The remote sends out the stream and the system acts per it's firmware.

My Sanyo remote sends IR, whenever I push a command button,
(vent angle control, Ions, fan control, temp change & etc) or every 5 minutes.

In the event of a short grid failure, the Sanyo will come back on and shut down.
But, within 5 minutes, the IR remote will sent it's bust and return the System to it's mode, prior to the grid failure.

If the remote's battery dies, the IDU will switch to using it's built-in thermostat.
But, if there is a short grid fail, the system is going to stay turned off..
Which means that the Fall season is a good time to replace the batteries..



Anyways, I was thinking if you could record all your standard command busts on a PC disk,
then your control program could just pick out the right file and transmit it with an IR LED.
Of course, the PC would need a room temperature sensor.

And the remote control would have to be blocked from interfering..

I'm pretty sure that I could get a wired thermostat for my model Sanyo.
It would require installing a wiring harness inside the IDU..
But, since I have a remote, (and a back-up) I don't see the need for a wired stat..

One other way to intercede into link using the remote,
is to add a temperature change generator to the remote's sensor.
A simple device to trick the remote into thinking the room temperature
had changed, would cause it to send new commands to the IDU..

Like if you had a solar GTI and you wanted to AC to really crank hard after 10AM on a sunny day,
you could place the remote on the rug, in a spot that starts getting sunshine at 10AM.. :)

Here it is. The device that interfaces from the TTL logic to the power leads is the HF6 3EB - probably a custom device as I can't find any reference to it anywhere. The rest is just basic RS232 to TTL level conversion stuff.

The CUT is where I break the comms from the internal unit to be able to send my own commands.

The CLK signal from the HF6 doesn't appear to be doing much as the data isn't synchronised to it in any way. It runs at 100Hz. I may be wrong but for the moment I'm not worrying about it.

Nigel

Xringer, if you aren't going to dig deeper like I said you're just going to have to trust me when I say that it's almost impossible to control a mini split with an IR blaster. Both AC and IR blaster manufacturers have been talking about this for years and to my knowledge no one has managed to get it to work.

It's a short burst.. Maybe running at 44khz, giving it a lot of data..
Here's an HD video.. (17.5 mb)
Sanyo ASHP IR data video by Xringer - Photobucket

Maybe I can look at it in slow mo and see more?

Although it's not the method I'm using I would tend to agree with S-F. In the thread you pointed us to on refrigeration-engineer the reason he didn't follow that route was lack of feedback. The problem with remote controls is they are one-way only so yes, I'm sure you can emulate some functions but you can never guarantee the status of the machine before sending the command. The only thing you could assume is that it is on so send the command to turn it off and start from zero.

The other problem with IR is it's light so if the remote isn't in view of the machine it won't operate it. There are machines that have a mode where the thermometer is in the handset and they tell the machine what the temperature is where the remote is placed, thereby controlling the machine, but I guess they must have some fallback in case of communication failure (as you described Xringer).

You'ld be very lucky to see what is going on - an oscilloscope or logic analyser are the only way. You'll then see something akin to the picture below. From there you can start analysing the pulse sequence/s.

So I thought I'd try to find out what I can about my 9K BTU sanyo mini-split...


This is the indoor unit with the air-filter shroud removed...

This is the diagram on the wiring cover...

Here's a close up of the wires...

This is the DC voltage measured from ground to the data wire...

This is the AC voltage measured from ground to the data wire...

Question for Nigel... what frequency is required to be able to analyze the data pckets?

-AC

The only answer I can give you is that it could be absolutely anything.

What you need to do is open the machine up and find out where the data wire goes/what it connects to and based on that you should be able to drawn out a bit of the circuit at one or other of the ends. Then you need to know what voltage it's all working at; normally it will eventually reach TTL levels (0V low to +5V high). Then connect an oscilloscope or logic analyzer, capture the data trace and from there you can deduce the operating frequency and from there the baud rate of the data.

If you're lucky it will (as in my case) turn out to be a standard RS232 speed, you may need to analyse the data frame to determine what the data structure is, stop bits, parity bits etc. as there are many possible combinations. In my case the Daikin was 1 start bit, 2 stop bits and odd parity and running at 1200 baud.

A cheap logic analyzer is probably the easiest way to capture the data frames for analysis - you can find them on ebay.

It's a challenge but can be done. If you have no electronics/software (you will need this next) knowledge then you'll probably need to enlist the help of someone who does.

Nigel

If it's standard RS-232 protocol, I have a TEK 308 logic analyzer.
Has a serial mode for RS-232.

You'll probably need to build a level converter interface (something like in my schematic using MAX232 and MC1489) to interface to the 5V logic - RS232 is +/-12V signalling so you can't connect directly from the RS232 to the machine.

Actually, with the analyzer it may not matter as it may be able to work at 5V.

You will need to trace the circuit though as I wouldn't advise connecting anything to the wires that go from the internal to external units as they are most likely at line voltage.

Nigel

That was what I was trying to determine when I read the potential from ground to the data wire with my multimeter.

The DC potential was 14.77 volts and steady and the AC was not steady and about the 0.2 volt level.

I have a boat anchor scope that I will double check the situation with today.

-AC

I think it's likely an RS232 level.. Or maybe a modified version that runs 0.0v to +15 volts.?.
I've seen a few of those. I've also seen some devices that had 0.0v to +9 (even +5)
and they worked just fine, talking to 1488 & 1489 chips..

The RS-232 standard defines the voltage levels that correspond to logical one and logical zero levels for the data transmission and the control signal lines. Valid signals are plus or minus 3 to 15 volts; the ±3 V range near zero volts is not a valid RS-232 level. The standard specifies a maximum open-circuit voltage of 25 volts: signal levels of ±5 V, ±10 V, ±12 V, and ±15 V are all commonly seen depending on the power supplies available within a device

I've had a couple more hours free to play a bit. I've now tidied up my program and removed loads of duplicated stuff, I've also cracked what is going on in some more of the frames.

I can now reliably communicate with the machine (it was a bit flakey before) and turn it on/off in any mode I want. I've also found the bytes that report the status of the compressor and fan. I've attached a photo of the main screen of my program.

I've ordered a PIC prototyping board that has a 16F877 processor, display, keypad, RS232, Temperature sensor and more off of ebay. My plan is to use this as my controller (no point building it from scratch as the built board is only $42 including shipping.

Nigel

Minisplit COmmunications
 

This is some fun stuff!! one of the members here found me on a Prius forum.. 3 years ago i did a lot of work on this with CHIGO branded minisplits to use in my Home automation system...

CHIGO is sold under Grunaire, amcoraire,turboair and other names.. These units actually have a connector for a wired control that can be soldered to on their main board...

unlike Daikin, or mitsubishi these things are not designed to run in a networked environment .. whereas daikin and mitsi have their own networks and computer control interfaces available for purchase..

my original project was so that I could control these units in a non standard way for z ducted zoned HVAC system in my house.. I not only wanted 1 direction control but I wanted to get feedback from the indoor unit;s room temp sensor... as my idea was to "feed the unit" its indoor temp from a micro controller..

I ended up using zbasic.net micros and creating a control board that has run them for 3 years now.. I never got into the indoor to outdoor comms much.. although I did get frames and start decoding them by picking up the signals to and from the indoor board right as they came off of the micro and before they went through the optos and superimposed on a higher voltage (30 VAC) line.

I can surely share any information you guys are interested in.!

couple things i found with the chinese units.. one is that the comms protocol really attempts to match IR remote streams.. they use the same algorithms and just apply the characteristics to wired lines ..TTL levels at the micros themselves. (in my case ATMEGA8 on Chigo units)...

the data streams were sent and then sent again inverted for integrity checking...

ie 00000111 and then right after 11111000.

they used a Pulse distance encoding style...

to start I'd get a 20 ms low... then a 5 ms high... then the data..

a "1" was a 2.1 ms high... then a .768 ms low (spacer), a 0 was then a .768 ms high then a .768 ms low (spacer) and so on.. 8 bits per word in this manner.. my units sent 5 bytes.. and the same 5 bytes inverted for a total of 10 bytes...(the byte and then its inversion right after)..byte-1...byte-1 inverted... byte-2.. byte-2 inverted etc

each byte being bit mapped such as 3 bits of 1 byte for the mode, 5 bits of one byte for say the setpoint, 2 bits of another for swing, etc.. I mapped out most of the registers.. but many i didnt care about...

im pretty sure each manufacturer uses a different algorithm.. but I do know that the IR remote commands for many of the chinese units are similar in how they do it just different bit maps for the commands..

I also was succesful in learning the LONG IR remote commands and controlling them with a global cache GC-100 box.. I did that for a friend who didnt want to go through building boards and the like...

the physical installation of my units is such is completely custom in that I disassembled the indoor units and built my own coil boxes and installed them in the ducting of my home behind zone control dampers.. one unit for each of 3 zones.. one central blower.. BAPI-HVAC controls static pressure and air velocity sensors allow me to control the VFD running the blower to maintain proper and desired CFM across each coil.. I allow the units to do their own thing to maintain their own coil temps and such.. I send the units their setpoints and mode.. and i use a digital pot to skew the indoor room temp sensor.. as Mini-splits were designed to be installed high up on the walls they are designed to turn on and off at wildly varied temps.. heat mode shuts off when its room sensor is 3 deg C above setpoint.. cooling at 2 deg C below setpoint.. that wouldnt fly in a central system.. so I fake the room temp based on actual to make the unit think differently... the digital POT faskes the thermistor and I read back what the unit thinks its indoor temp is via the comms link to adjust properly..

for 3 years now the system has run very well except for defective Capacitors on the PFC boards of the units.. easy fix to replace the MOSFETs and caps that died in the first 6 months of service.. no more issues after that..

I havent really tried to measure the COP on the heatpumps but I do know since I put the system in my comfort level went up and my bills went way down from the 2004 10 SEER A/C that was installed when the house was built so I let that speak for the success..

the HVAC is just part of a complete home automation system running on a mixture of windows (Homeseer) and some custom linux stuff..

hope that helps you guys out a bit.. I love this kind of stuff its a BLAST!
-Christopher

Question about schematic...
 

Acuario,

I'm about to build the interface as in your schematic or similar.

I found this part (DS275)...


...and I was wondering if it would be suitable for this project?

Best,

-AC

In theory it should be fine. I did have problems trying to use 1 chip for both TX and RX though, that's why I reverted to 2. Try it and see - if it doesn't work try a MC1489 on the RS232 TXD leg.

Nigel

That probably works if you really have RS-232 on the other end.

You have a scope, what voltages did you measure on the port when
transmitting? What's the quiescent voltage when not transmitting?

What part of the problem are you trying to solve?
If it's serial data and you want to look at it, why not hook it to
a real serial port? I understand the trepidation of hooking your
$2,000 laptop to an air conditioner, but you can buy laptop
computers at garage sales for less than the shipping cost of the chip.
Ditto for PalmIII PDA's with serial cradles. The newest PDA's don't
have serial ports, so stick with the old stuff with a serial cradle.
FREEWARE comm sw
is available for both.

Don't be put off by the price sticker. It's not unusual to get old
laptops marked $50 for a buck by the end of the day.

I've interfaced a bunch of computer related stuff.
A diode will connect a PIC processor to RS-232, you just have
to set the compiler directive to invert the data.
A pair of transistors makes a great inverting interface.
0-5V works fine on most serial inputs with short cables.
Never had that not work, but I've never interfaced an air conditioner.

You may be able do do something interesting with the IR port.
Like receive the remote and send it out the serial port.

Make it work with a computer interface, then when you're done,
convert it to a microcontroller.

In my case I used a Logic analyzer to pick off the Signals on my units..

if you look at the boards of your unit and are trying to interface to the indoor-outdoor Comms link that all ends up at 5 volt TTL levels to hit the micro when all is said and done.. past that it is put through transistors and optos and boosted up onto a higher voltage carrier to deal with the crazy EMI around a VFD motor drive, and also to beter handle surges that occur on a line...

since most of these units arent capable of calculating LRC or CRC checks on their data streams they either rely on it to be correct all the time or invert it after the initial send and if they dont have a match. discard the record...

the Logic analyzer I use is a Salae LOGIC and it will capture data for you so you can go back and analyze what you are getting across the comms line...

the other thing to remember is that these units do electronically what traditional units do mechanically or with temperature change, etc.. they are engineered pretty tight... if you have the inclination to directly control your compressor drive, expansion device opening, outdoor and indoor fan speeds then you are a brave one..

having worked on both computers and HVAC i can honestly say the algorithms inside these units are pretty much dead on as far as the mechanics and thermodynamics of it all...

they know more than you think they do.. my units for instance have 5 temp sensors outside... 3 on the coil, an outdoor ambient, and a compressor disscharge.. and 4 on the indoor.. 3 on the coil and room temp...

the VFD board provides feedback to the current being pulled by the motor and the voltages at the motor.. so now with all that info the unit can pretty much calculate the line pressures low and high...

in playing with them they will do some wild stuff to keep themselves running.. ie kill the indoor fan and it floods the evaporator and slows the outdoor fan, raising the head pressure and evaporator pressure so it wont freeze up. eventually it shuts down as it knows something is wrong after 5 or 6 minutes of freeze protection...

kill the outdoor fan and it ramps down the compressor and indoor fan in hopes it may still gain some cooling.. after a couple minutes it shuts off if its hot enough out..

as I mentioned in an earlier post, getting feedback as to what the unit is doing wont be possible via the IR port.. the IR is ONE way on most all A/C units.. it sends a LONG code each time a button is pressed... ALL parameters are sent in each remote command.. mode, temp.. fan speed, swing, pitch, etc are sent at each remote press to keep the remote in sync with the unit..

if you take the remote into a closet and jack up all the settings. then walk out to the unit and press just ONE button, the unit will then take on ALL of the settings the remote has on it.....

cool stuff!
-Christopher