I was out there this AM looking for a drain. If you look under the hood, passenger side of the engine compartment, you see the Fan Motor and the A/C Drier (black coffee can) with metal lines going into a black box that's the Evaporator Core of the HVAC system. Heater Core's in there too, somewhere...
Anyhow, that location and our drip pattern tells me the Drain you seek is on the bottom of that Black Box. In another Ford we own, that Drain is only a divot in the seam where two halves of such a box come together. Not an actual fitting. So such could be the case with these E-Series. I just don't know, but I was under the hood, under the coach, with flashlight and mirror. See if you can find an agile person with small hands to reach beside the inboard (engine) side of that Evap Cabinet, and feel along the bottom. If you find a hole, probe it with something kinda flexible like a ZIP Tie. Don't go ramming a coat hanger up there, could puncture a core.
Didn't find anything conclusive. Also didn't find the Resistor Pack. It might be inside, but I CAN tell you it's in HVAC air flow someplace.
Tapped out. Wish I had more.