7000 heater control

I cant get the heat to come on. Checked hoses, no heat on them. I'm assuming the contoller in the cab is hooked to the valve that controls coolant flow.

Anything I need to take note of during disassembly. Service manual is on the way, but I want to get started.

Thanks in advance,

Rick

Warmed up tractor high idle. Hyd and engine oil good and warm, coolant warm, but not too hot to touch. Still no heat.

Noticed upper radiator hose was warm. But the coolant filter lines were cold as was filter itself. And of course heater lines were cold.

The heater and the filter come off the same tee right before the lower rad hose goes in the block. They both return at the thermostat. Should one flow into the other versus two separate runs?

Seems like the two runs (heater and filter) are not flowing, is this possible.

Thanks again,
Rick