HVAC issue with our 07 Discovery

Have a Denso HVAC with a rotary temp dial. I crank the heat to full but just get warm air. Now when I open the hood One hose feels lukewarm. Looking over some Denso service manuals it appears that Denso does not use any kind of valve on the heater core. Appears it could possibly be a blend door that allows warm air into the cab. So I assume water continually circulating thru core even when cooling. Am I correct on this theory?

I have two gate valves on the heater lines back at the CAT. Both appear to be fully open. Is it possible I could have a closed gate valve or an airlock on the heater end of the coach?

Wondering if any others have torn into these HVAC setups. I'm on a Freightliner chassis.

Thoughts?

RM