No interior heat?

Hi all,

my ride is an 85 300d

I've been trying to figure this out for sometime and now that it snowed last nite it's become a bit more urgent.

I get no heat at all not thru the vents or defrost

I've replaced the monovalve, and the coolant is filled to the arrow.
blower is strong still just cold air all the time.
I also checked the aux pump and that seems to be humming right along when it's getting power. checked the power going to the monovalve and there is power there as well.

if it's the heater core how do I get to that? do i have to remove the entire dash?

thanks in advance for any input.