I have bought two second hand "HRV" brand units which both work by themselves but I can't figure out how to link the two together so I can have both fans running simultaneously. 

I have one fan slaved off the other for power and I've plugged in the network cable from one to the other but nothing happens to the slaved unit. 

I be interested to see how 2 units are connected together in other situations since I don't have a wiring diagram or installation instructions to work from. 

Thanks in advance. 

Tia