98 taurus

.. can you READ!!???

If both hoses are hot, and the blend door works, your core is likely plugged! Garden hose on it means nothing, it takes only a few open ports to produce good flow.

- - - - - -- - -- - - - -- - And A/C has been used in defrost for decades, as long as ambient temp is over 40 deg.

ALSO!!! Had you recently drained, or had low, coolant (just before problem)?

If your heater core connections are "top and bottom" oriented, make sure that the top one goes to water pump, otherwise an air bubble can linger in the core and 'block' water flow.

Air does NOT like to 'suck down'!

How do I get the Air bubble out of a Heater core?

Larry

If it IS an airbubble problem..

Then Install a flush TEE in the hose from the top nipple, warm the engine up and shut it off. Wait a few minutes and using visegrips and small blocks of wood as protection clamp off hose on engine side of tee and loosen tee slowly to let any air escape...

May have to repeat this several days in a row.

But as said, your core May be blocked by crud.