Originally Posted by Dudupatty
The vehicle Barrett was at 12.1V and as soon as I hit the switch, it went up to 13.4V and the fan on the breaker kicked in. Is that normal?
I'm not sure anything is ever "normal" on a motorhome. Always something that's different. But in your case:
The 12.1 V reading is the voltage from your house batteries. That's low. It should be 12.5 to 12.6 if they are fully charged. I usually don't get too concerned until that reading drops below 12.1 V. That reading will vary depending on the charge of your house batteries.
When you hit the switch, the electricity is then "allowed" into your motorhome. At that point, the built in charger recognizes your low battery levels and kicks in to charge them. A 13.4 V reading is indicative of a trickle charge. Again, that reading may vary depending on your charger and how low your battery charge is. When the charger kicks in, the fan will start too.
What you are describing is seen quite often - probably about as normal as it gets. With that said, this is very generic information and there certainly can be other suggestions too.