So does it blow heat through the floor vents? Or no heat anywhere in the cab?
The only way to have no heat but all the vents blowing air is a plugged heater core. I would recommend replacing that. Air you sure you felt the input and the output hose? Did you check them before the whole engine compartment was hot from the engine. If it was me i would swap the heater core though. I hope this helps. If this information was helpful please click the accept button.
The heatercore is surrounded be a plastic box with the doors on it like you say. You might be able to access it through the glove box by removing the glove box. Or you will have to go at it from under the passenger side interior. Please click accept and i will continue to try and help you with this issue.