Daikin Skyair Communication Between Indoor and Outdoor

[mburns]

Just interested to see how the communcations between the Indoor and Outdoor work, or the number 3 terminal.

I've have tried looking through quite alot of Daikin data to try and gain some insight but not not avail. I've been told to test to make sure i have at least 50V DC on this line but i always seen to have a much higher voltage than that. It does change and drops voltage then raises voltage every second or so and repeats that cycle (that is testing to a DC negative and also trying an AC neutral to see what readings i get.) e.g Drops to 180v then raises to 200v and repeats that cycle and then i put it heating or so and register different voltages.

I've seem to come the conclusion that fluctuation in voltage cycle is the indoor pcb sending to the outdoor pcb then vice versa.

I may be completely wrong but wouldn't mind someone elses insight! Thankyou

[Tayters]

In normal split communications (not just Daikin) the signal is based on the 240V AC supply. One unit will use the positive half of the cycle and the other unit will use the negative half.

When communicating the units pulse the relevent half of the cycle on. The other unit see these pulses, it doesn't matter how high the voltage just a negative or positive pulse. The pulses build up a binary signal which it then decoded by the other unit.

Cheers,
Andy

To test comms you can disconnect the signal wire, measure between neutral and the wire and also between neutral and the terminal block you've disconnected the wire from. This way you are testing comms from each unit individually. Use the DC Voltage scale and you will get +ve or -ve voltage 70 to 100 V. Comms may only work for a couple of minutes from power on.

[mburns]

Thanks Tayters that does make a lot of sense.
Just one thing i'll ask, you do say measure from the comms wire to the neutral on the terminal block or the outdoor comms terminal to neutral to verify the pcb's are talking. I'd be a bit suspect with that reading because it's 240v a/c neutral on the terminal block and you would get the wrong reading. I'd be more inclined to get access to the pcb and find the DC point and reference to that? Correct me if i'm wrong