On the back of the A120 there is typically a CNC interface port. When you purchase the unit from us we provide you with a cable that comes off of that port with two pairs of wire that we use. The first pair, pins 3 and 4, are for the torch on signal, which hook to the connection on the back of the AVHC labeled Torch. Pins 12 and 14 are for the OK to Move signal, which connect to the OK to Move port on the back of the AVHC.
If you have this connection made, and are still having problems, please contact us and we can start diagnosing if the plasma cutter is not transmitting the OK to move signal.