[2BirdDogs]

Paul,

I don't know how/why the black box is in the circuit. But I recognize that black box. It is a common delay device used on home air con systems to prevent the compressor from short cycling. It is typically delay on break, meaning that once the circuit is broken, a timer starts and it will not energize for the specified time. It appears you have an adjustable version.

Can you trace the wiring coming out of the black timer device to see if it indeed is going into the clicking relay?

Is this a new phenom? And I assume you want it to stop?

Thank you Richard. 

Sorry for delayed response... I had a family need that took me away from things late last week until today. 

1. I will trace the wiring tomorrow and report back. 
2. Not a new phenom. I noticed the pulsating when we first got the coach 3 years ago but I just noticed the association with the relay in the electronics bay a few weeks ago when it was quiet in the coach and I happened to hear the relay clicking through the floor under the dining table (at the same time I noticed that the aquahot electric element was energized and the two bathroom heater fans were pulsating).
3. Yes I would like to figure this out and stop the pulsing fans.

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Has there been any repairs to either the HVAC or the aqua hot recently?

Thanks Jack.

NO repairs to either HVAC or aqua hot recently.