What's an aircon?
how/ what is the best and most economical way to control all the aircons remotely as the arduino only has 1 pin used for sending IR signals.
...you could possibly also Mux all of the IR LEDs together and control it using 5 pins (Signal out + 4 Mux channels)
If hard wiring isn't feasible or you can't get the library working on multiple pins then you could use an Arduino per unit.
What if you use a Mega instead? Then you'd have plenty of PWM pins to support 1 pin/unit and not need any external hardware.
1 x Arduino per unit would be costly option for me unfortunately.
If worried about signal integrity:Run CAT5 type network cable from central processor to each.+5, Gnd, and +/- RS485 signal. At far end, MAX488 chip to turn RS485 back into 0-5V signal to drive the LED.Central processor then just needs a daughter card with RS485 drivers and connectors for the cables.4mA enough to drive the LEDs?http://www.digikey.com/product-detail/en/MAX488CPA%2B/MAX488CPA%2B-ND/948031