The ECC units have a blower switch that has variable speeds, ie. not 1,2,3,4. If this is the case, check the level of antifreeze. Make sure the vent selector and blower speed are in the auto position before you put the key in the ignition.

You could remove the kick panel next to the gas pedal and feel the coolant tubes going to the heater core and make sure they are hot (and not leaking).

Because you say the engine temp is OK, it may well be that the temp dials are broken. For both of them to break at the same time will be quite rare, but possible. If this is the case, a new ECC unit will be needed. Junk yards are full of them (1998-2000).

Or is it the simple center dash vent is open to outside air?
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