When the ignition is turned on the aqua hot register fans in the dash are turned off and you then get heat from a different fan that blows through the heater core that is heated by the engine. The engine is heated by the aqua hot pumping engine coolant through the engine. It is a separate loop from the aqua hot fluid.
Would that system be adaptable to my 97?
For sure my 2001 U320 has the exact same setup in the dash for Aqua Hot and engine heated hot air. Having had the LP Gas heater systems before, I would not ever want to go back to it. Do not know all the ups/downs or ins/outs of the A-H system, but from my experience, will stick with the Aqua Hot and keep smiling.
The LP Gas systems are cheaper to purchase, but I find the Aqua Hot gives the total warm & fuzzies for me with the 4 adjustable thermostats and comfy everywhere, no hot or cold spots.
Just for the record,
The Primus system runs like the Aqua Hot through the dash but, it is controlled by the existing dash controls and fan.