Opened a support ticket but that's been several days so posting here.
It was my understanding that this is tested done per this:
Theory of Operation:
The two AC line monitor chips act as opto-isloators. The presence of an AC voltage potential relative to ground on either L1 or L2 will result in a state change from High to Low appearing on PD3 and PD4 of the Microprocessor.
The circuit tests both stuck relay (voltage present when there should be none) and continuity to Ground (voltage present when it should be). Stuck Relay is tested whenever the relay is open and Ground is monitored when the relay is closed.
So the 2 times I got this error the unit was not in use and in fact it had not been in used for at least 2 days.
So there is no way there was a stuck relay with a unit that is on standby and for sure the relay is not stuck and was not even in use so there is no way it could be stuck.
The cable was not attached again unit was powered, not plugged into the EV, just idle on the wall.
Since the other 2 unit have no issue there must be an issue with this particular unit what could be the issue?
We would reccomend checking the ground connections for the AC cables, EV cable and the connections between the OpenEVSE controller and the ground plate. The AC detect circuits are just a LED and detector, so if the issue is not the AC detect lines it has to be the ground.
OK checked all the grounds. Note this happens when the EVSE is just sitting idle on the wall not even connected to the EV. So that would eliminate anything on that end being the problem but checked them anyways.
Measured between all connections, cables, board, plug, all show 0 ohms on my meter. Just for giggles I measured from the ground screw of the board to an extension cables ground in my garage. So that would be a 25ft extension cable plugged into an outlet in my garage, that goes on 14g to the main panel, then back to the 14-50 on 6g, then hits a 6g 30 ft extension cable, to the EVSE cord. All that and we have only .9 ohms. So I am going to go with the grounds are rock solid.
So remember this only happens when the EVSE has been sitting unused on the wall with nothing connected just the AC. So not sure how it would think there is a stuck relay when the relay is idle and not even in use at all. All cables meter 0 ohms all connections are solid even if wiggled. Cable to EVSE is out of the equation since this only happens when it is not even connected.
I am more thinking a flaky control board unless you have other ideas?