My 1998 1500 has no heat...It also blows A/C when the Defrost is turned on...you can hear it come on.

Fluid level is good.
Engine temp is normal.

Anyone have any ideas?

TIA
Dan.

Two things come to mind.

The blend door is stuck or the heater core is plugged.

On several occassions in the past, I have found the control unit was bad.

Ditto on the control unit. They are prone to go bad on certain vehicles.