Hello Gil J,

The 2 garden faucet style valves are definitely Prevost. The will be soldered into 1" (+-) copper pipe.

They are both off of the engine coolant and run to the dash heater core, similar to car. If you have Prevost Over-the-road heat and AC they will run through that core as well.

The core is located in the lower dash, roughly at the passengers feet and has the AC core on top and a duel cage blower underneath.

These 2 valve shut off or open hot coolant to the dash heater core. One valve, I think the upper, is for supply and the other is for return. The related piping runs forward and back in between the frame rails in what would be the ceiling of the bays, to behind the front bumper.

At the front bumper area (on your back looking straight up) is the "hot water valve" or liquid solenoid, that is activated by the heat switch at the dash. If heat is called for the valve under the bumper will open and direct coolant to the core in the dash. If heat is off, the coolant is by-passed straight back to the engine.

The valves in question isolate the forward flow to the engine area only.

Most customers leave these valves open, unless the solenoid under the front bumper is stuck open, or the diaphragm is torn, and the dash area is unintentionally receiving heat. In which case you can stop the flow by closing one or both of the garden type vales in back.

The ball valves are hard to tell without tracing, but to the water heaters as noted above sure sounds right.

Hope that helps,

Pat Sprenger
Coach Pro LLC
800-918-7172