Several years ago rewired 2 or 3 outlets and ceiling fan/light with new 20A circuit in a bedrm in an old house for customer. Old wires abandoned and not touching new RX, they called back weeks later saying AFCI occasionally trips while using window unit AC. I replaced AFCI, also checked my wiring for anything too tight or ground and nuetral touching in boxes-all good. They just called last week saying after 2 wks of using the AC it tripped the AFCI, I told them I think its the AC but told them to switch circuits using extension cord and other bedroom AC as I had also rewired several outlets in the next bedrm also. Still waiting to hear from them but seems to me it would be the window AC but it doesn't do it all of the time though.