[Schurkey]

Originally Posted by ASJT3

I'm guessing this is what you meant by the duckbill?



It was clear and not blocked. I removed it and did the same test, water still leaks in the cab.

Yep, that's it. Sorry it wasn't the problem. Can you look up inside the hole in the box that that fits into? Is the BOX full of sunflower seeds/cottonwood fluff/mouse nests, etc?

Originally Posted by aleekat

I would look for a welded seam in that cowl that normally is sealed and painted over. It may look intact, but can crack over the years and allow water to seep in. I've used some exterior 100% silicon 30yr chalk with good success.

With the drain verified, and the heater plenum not filled with debris, this is probably the next step.




For whatever difference it makes, does the truck cab stay hot in the winter and cool in the summer based on heater/AC use? My cab was cold with the heater on, and warm with the A/C running. Had a MASSIVE outside-air leak into the cab where the steel of the body transitions to the plastic of the HVAC blower housing. Foam gasket completely rotted out, and it was a hateful job to replace. The '88 service manual gives the WRONG instructions. I had to refer to the '88 service manual SUPPLEMENT for correct procedure.