I'm using the circuit below in a custom PCB to switch on and off an electrovalve.
I assembled partially the PCB, just to verify some voltage across the triac. I didn't connect the MOC3021 and R40 at the moment.
I plugged the 230V main AC and measured the voltage across the two terminals X10-1 X10-2, and strangely (for me) I measured 148 VAC! Note that GND230 is only a label to distinguish phase and neutral in the schematic. I was expecting that, since the gate is disconnected the A2-A1 was at high impedance and any voltage would have been measured between A2 and A1.
As extra test I connected a bulb lamp between X10-1 and X10-2 expecting that it would switch on with 148 VAC. Instead, when I plug the 230 main AC, the lamp is lighting for a very short time (<0.5 sec) and then it switch off. In this condition the voltage between X10-1 and X10-2 the value is zero as expected.
What happen that I don't understand?
As a secondary question, what could be a right value for R40?