hi dean,
there are many different configs on the coolant lines from the engine to the front. (on 8v92's anyway)
some have two valves at the back, most have 4. the ones with two have one set that usually just control the inlet and outlet to the hot water heater.
mine only has two. as it comes off the engine, it goes to a solenoid controlled pump mounted on top of the frame rail right in plain site in the drivers side engine compartment. the solenoid opens the valve AND turns on the pump at the same time. it pushes coolant up towards the front.
in the middle of the coach in the ceiling of the bays, you will find a maze of coolant hoses. they are a series of Y's and i check mine once in a while to make sure the hose clamps are tight.
on mine, i have a heater core under the bed with a fan that is controlled by a switch on the dash. there is also a heater core in the drivers side wet bay with a fan that is turned on by a switch on the dash.
i also have my hot water heater fed from it as well as the heater core up front.
the y's enable a return path for the coolant even if any one line is turned off or plugged. my hot water heater didnt work initially and i found that the return and inlet coolant lines had been reversed at some point. when i switched them back it worked great. in fact too great in that it was too hot so i put a tempering valve in.
unlike any others i have found, i also have a solenoid controlled pump at the front to push the coolant back to the radiator. it turns on at the same time as the one in the rear.
both pumps and valves are controlled by turning the heat lever on the dash heater/ac control towards heat. newell installed a microswitch on the lever mechanism that turns it on after it is barely moved to the right. if you listen while moving the lever with nothing on in the coach you can hear the microswitch click when it hits the turn on point.
to get hot water from my hot water heater from coolant, i have to have the lever turned on. the problem is that the same lever opens the slide valve with a cable that opens the water to the heater core up front and your vents get warm.
when i put my new control unit on i transplanted the microswitch from the old one and tried to make it so it was barely on when it turns the switch on. sometimes i want hot water when i dont want hot air...like when it is not cold out.
some people have solenoid controlled valves at the bed heater core or bay heater core. if my pump is on, those two heater cores on mine get hot. if the fan switch is not on, it is not blowing hot air.
the front pump that i found is behind the plenum behind the front cap and you can only see it if you get a few of the plenum hoses off. that is also where the slide valve is that is actuated by the boden cable that runs from the lever control on the dash.
i drew a map of my hoses but since each one is different, you will have to do that for yourself.
btw, the vent hoses are lightweight flex hose and are getting brittle with age. i have had to seal up leaks on a few of mine.
hope that helps some. call me if you want me to talk through it.
tom
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