This unit is under the bed in my U320. When I plug into shore power this unit hammers itself. I watch the readout board in the coach and it just comes and goes until this stops chattering. Nobody seems to know its purpose..well at least me and the electrical supply house. I just had the transfer switch replaced thinking that would do it...no luck..
That appears to be the cover for your built in surge protector. Now remember that is just a WAG
Mike
I would think that this is an under/over voltage protection device. If you plug the coach into a good stable source with everything turned off it may stop the chattering. If not it's faulty. You can disconnect it and replace it with a new power protection device. Here is a link to a company that makes the one I have which is a built in unit.
Keith
Rv Surge Protection | United States | Progressive Industries, Inc. (https://www.progressiveindustries.net/)
It is a line monitor.
Where can I find a Power Stop Corp. Analog Line Monitor ALM-50HW? (https://www.justanswer.com/rv-motorhome/4lfmu-find-power-stop-corp-analog-line-monitoralm-50hw.html)
It sure appears to be something that may have to be eliminated..not sure yet. I will put my surge protector and the shore power supply plug and see it that keeps this one from chattering. I'm not sure if this puts the power up on the monitor in the coach...I gotta have that to see what's going on...
Keith I have one of those...and I will go home and put it on the stand. And your right..I had the thermostat on for heat pump..did not know it. So that could have been some of it..
This is an Analog Line Monitor, which (though lord I can't find any documentation on the thing) I have the impression is the old-school version of an under/over voltage protection device... without seeing the inside I might suspect there are a couple of capacitors and probably a small transformer in the box to help iron out dirty shore power. Just a (somewhat) educated guess... and I'm not sure in the least whether it can be just pulled entirely out of the system or replaced by a different device buuuut here's an eBay link to a new one: power stop corp alm-50hw analog line monitor | eBay (https://www.ebay.com/itm/power-stop-corp-alm-50hw-analog-line-monitor/323644051784?epid=17023307575&hash=item4b5ab05148:g:WaQAAOSwM9xbiyaf)
Good luck!
I bought it...Thank you.