R21-EC house battery charging problem

[tjcouch]

The boat: R21-EC 2015 Volvo

The alternator charges the air-con batteries, the cranking battery, but not the house battery.

I have read all of the related posts I could find.

I have cleaned all terminals.

I have replaced the battery.

I have replaced the charging relay.

The on-board charger returns and maintains the house battery to full when on shore power. But as I cruise for a day the fridge, VHF, GPS, and the thruster cause the voltage to slowly drop per the voltage monitor on the GPS.

With the engine running I get 14v to all batteries, EXCEPT the house as read by a handheld voltmeter.

I had high hopes it was the ACR . . . but unless the new one was also defective . . . highly unlikely. I am at a loss.

 

[Pilotnavigator]

What voltage does the plotter show, I have my plotter set to display the voltage as well as the speed etc. on the right side. This way I can monitor the alternator output. After a few minutes of running the voltage should show 14.1.
Have you ensured the thin white wire on the ACR is connected to negative bus? And is it connected to the ACR? Mine fell off the ACR one time and I only notice when the plotter showed 12.5 volts while running the engine. Also I modified my alternator output to charge directly to the house. Remove the short red wire between the alternator and the starter and connect a “fat” red cable from the alternator post to the house positive bus. This will put most of the current to the house and let the ACR charger the starter.
This last part should not affect your system and is only a nice to do. But I am sure you have a bad ground on the ACR. Prove this by measuring the voltage on the starter battery with the engine running and it will be 14 or so if the alternator is good. You are just not having the ACR closing down to connect the charge current to the house. The ACR needs to have a ground wire.