Lights dimming

Think of your batteries as a buffer. Even on shore power they will store power and if your converter doesn't have enough juice it will supply that amperage to help out. When the amps fall off the converter takes back over and the batteries top back off for the next time. If your batteries are going out they can't supply the needed amperage to the system. That makes your converter work extra hard and your voltage will dip causing the lights to dim and maybe even flicker.

I vote batteries are toast

Chris

BATTERIES!

when I experienced the same symptoms, it was a bad converter. I read converter output to confirm. All is well now.

I agree that you probably have a weak battery. The startup current on a DC motor is quiet a bit more than the running current and could exceed the converters output. A good battery will supply this extra surge current.

Furnace fans are one of the biggest draws in an RV electrical system.

The shore power is relying on the converter AND the wires from the converter to the battery to do the job. Many many converters have been replaced, and of course when that happens the wire connectors are also tightened so it looks like the new converter fixed the problem.

Before you do anything, measure the converter output right at the converter. My lights were dimming, and I found my problem was just a loose negative wire at the converter terminal going to the battery. Tightened it up, and all worked just fine again.

I would definitely check the fluid levels in your battery. This is usually what happens when your battery has perhaps boiled out the battery fluids and maybe you now have a bad cell in the battery. A fully charged battery should read 12.6-7VDC at the battery terminals and when you hookup to shore power this same DC Voltage level should jump up to 13.6VDC telling you that your battery is being charged.

When on shore power the on-board converter/charger is attempting to charge your bad battery which may be the cause for the diming of the lights etc...

If the battery checks good then this could also be the first symptoms of a failing converter/charger unit....

You need to monitor your 12VDC voltages both when just using the batterey and also when you are plugged into shore power...

The 12VDC is changing levels on you causing the diming of things...

Just my thoughts and guesses...
Roy Ken