....Bah, just saw that Silver had mentioned the same thing after I wrote this..haha. Oh well I'll leave this up to reiterate his response.....
Not sure on yours (but likely) but on mine, an '08, there are the coolant lines that travel from the engine to the HVAC in the dash. On those lines near the engine and accessible from underneath the coach there are valves that allow the coolant to go to the HVAC, one for each in flow and return. It is possible these valves were never opened from the factory? They are used so that if the engine needs to be worked on and coolant drained you can close those valves and not have to drain out the entire system forward of the engine. If they were never opened you need to be wary of one thing. Were they opened when the engine was filled with coolant originally? If not then opening them may cause your coolant level to drop quickly as the lines fill and coolant flows into the HVAC circuit. Check to see if they are open or closed. They typically are yellow colored dial T type knobs. If you have had any work done, a tech may have closed them and forgot to open them again? The system may be full but the valves just simply need to be reopened.
On the same note for those that want some better dash cooling efficiency who travel in areas where you never need the heater, you can close these valves so that the a/c system isn't trying to overcome the hot coolant in the HVAC unit. Someone told be they gained quite a bit of extra cooling by doing that. I haven't tried it as where I am you can need heat one day and a/c the next!
Keep us posted
2008 Berkshire 360QS-40
"If you can't fix it with a hammer, you have an electrical problem"