documentation of M-Net electrical signaling and higher-level protocol?

[robthedude]

documentation of M-Net electrical signaling and higher-level protocol?

I've got a Mitsubishi electric system in my house -- it's a single system, with one PEFY-P36NMHU-E and one PUMY-P36NHMU-E outside, controlled by a PAR-30MAAU.

I'm not happy with the PAR-30MAAU. (For one thing, the temperature is off from the actual room temperature -- it says it's 63F when it's really about 69F. And it won't let me set it any lower than 63F. But since I would like the heat to go down to about 62F at night, I need to set it to about 56F, and as I said, it won't let me go down below 63F. I'm going to get this looked at, but in the meantime…)

I'm a bit of a tinkerer -- I'm an experienced low-level software engineer, and a friend of mine is a good electrical engineer, so we were wanting to see if we could create an M-Net control device to let us talk to the unit. But we can't find any substantial documentation on it at all.

I've found the CoolMaster product, which actually does what I want, but it's a bit expensive for me (though I may still get one). And I'm really interested in the challenge of engineering something.

Is it possible to get documentation on the M-Net protocol? Or perhaps get one of the CMS-MNG devices? Neither of us are HVAC technicians -- indeed, we're not really in the HVAC industry at all. But if we DID want to do that, is there any kind of Mitsubishi developer program where specs of this sort are documented? I looked all over the mylinkdrive site, and I found some high-level documents, but I didn't see anything low-level. Maybe I missed it though.

Any information would be very much appreciated.

[Brian_UK]

I would be careful about trying to run your unit at a lower than designed temperature.

The frost protection of the indoor unit might come into play as your try and turn an air cooler into an air freezer.

The 53°F setback temperature can only be used with certain models, such as PURY, PQRY and PUHY.

[install monkey]

indoor unit ,switch dipswitch sw1-1 to on, unit operates off sensor in thermistor- will display a lil controller to indicate that operation controlled via remote controller otherwise get thermistor values off sensor and stick a resistor inline to adjust sensing temp- try sticking a 1k ohm to see how the detected temp value changes

[robthedude]

I would be careful about trying to run your unit at a lower than designed temperature.

The frost protection of the indoor unit might come into play as your try and turn an air cooler into an air freezer.

The 53°F setback temperature can only be used with certain models, such as PURY, PQRY and PUHY.

That's not what I'm trying to do. I'm trying to run the unit in HEAT mode, but not actually HEAT the room until the temperature drops to 60F. Right now, the lowest I can set it is to 63F, which because of the other problem is actually 69F. So if I could set it to, say, 54F (which would really be 60F), then I'd be OK -- but as I said, it won't let me do that.

I'm not trying to cool the air below what it says. I'm trying to allow the heater to not run all night, because I don't need it to keep my room at 69F while I'm sleeping.

I saw install monkey's suggestion and I'll try that.

Of course, I'm STILL interested in M-NET documentation if anyone knows where Ic an find it.

[install monkey]

sw1 is a bank of 10 dipswitches on the pcb with the rotary address dials- do not adjust the rotary dials-theyre for the address of the unit- power down the unit and use a nail or small pointy object to flick the dipswitch- make sure you hear it click as you move it , power up and the controller should display temperature at controller height- if par 30 cabling is run in a cavity or in conduit then make sure the hole where the cable pops out is sealed, airtight as any draughts can influence the sensor

[stufus]

Turn dipswitch SW3-8 off and it will do away with a 7.2f thermo shift and allow your unit to control the space closer to set point.
The M-NET protocol is like pixie dust
Cheers
Stu