Without the exact model unit and some diagrams anything less would be a guessing game.
That said most of what you will find as far as fuses relays and controls will be located inside the aqua-hot unit itself located in the belly of the beast IMC.
When you pull the cover off the unit you see something similar to this
When my unit did what you describe I removed the unit cover and again this is what you will see or very similar.
I tested the fuses and they were all were good ..... Hmmm?
Then I started grabing and wiggling connections and all seemed fine, then I pushed on all the relays ( yellow arrows ) and Yahtzee!
...I here the fan come on.
The relays all were loose in their receptacles.
They have spring steel retainers that had most of their tension and allowed the relays to wiggle around and become loose in their receptacles.
I pulled all the relays checked for signs of overheated connections and their was none, so I tweaked the retainers clips a bit to hold the relays firmly back in place and all is well 2 years later.
These coaches take a beating as far as shock and vibration and are very prone to loose connections over time.