I have a 3-phase input in my home. There is 127 V between any of the phases and neutral, and 220 V between any pair of phases. The electrical appliances have 127 V, and the wirings are such that the air conditioners (that uses higher currents) of 3 rooms are connected to different phases.
I replaced one of them, and the new one needs 220V. I used the phase of the old one and another phase used for the lights and sockets of the same room (see picture).
It is working fine for some years, except that if I turn off the circuit breaker of one of the phases of the room (that used for lights), I have all kinds of unstabilities like blinking lights and beeping sounds from appliances. I need to turn off both S and T to properly turn off the energy of the room.
If only phase T is off, the sockets keep live. A voltimeter measures 127 V between live and neutral in the sockets. But an incandescent test lamp shines weakly as the voltage were smaller than that.
I suppose that somehow the phase S partially feeds T through the air conditioner wirings, but on the other hand, if the 2 phases were connected inside it, there would have a short circuit. There is a remote control for the air conditioner, and I don't turn it on during the experiment.