Lloyd,

There are coolant shut off valves on most of the buses. One is the flow to the heat source and one is the return. On your vintage I'm not sure if that loop is tied into the Webasco, but if it is, you may not be getting coolant to the heat exchangers if someone closed the valves. On my 97 Marathon, closing those valves stopped all coolant to the dash heater core, but I don't remember if the Webasco was in the same loop.

Jon?