No cab heat Allegro Bus 35RP

[Tahoejeep]

I've had motorhomes for 30 years, but bought my first DP, a 2003 35' Allegro bus, last August from a Tucson, AZ dealer. Freightliner chassis and a 2136 Cat. I guess it was hard to verify that the cab heater was working when it was 110 degrees out during checkout, because when I got home to Minnesota, no cab heat. With a hot engine, both heater hoses are cold. Both shut off valves back by the engine are open and I have antifreeze at the outlet valve petcock (with outlet shut). There's a vacuum controlled valve at the heater that closes on Max AC, and it operates correctly. I pulled that valve and it is clean and works internally. I also have antifreeze at the vacuum valve. Because the valve is clean inside, I assume the heater core is also good. Is there a water control valve inside the heater that modulates the heater temp? Or is temp controlled with blend doors?

I'd bring it back to the dealer, but am not planning to return to AZ until January. Any suggestions as to where to turn next?

[BFlinn181]

You might look for an owner added shut off valve in the heater hoses. This often done to stop heat from reducing A/C in warmer times. You could also remove the hoses from the heater core (under the windshield) to see if water is flowing from the engine.