Excessive condensation on windshield

You have moisture in your truck somewhere. Carpet under mat, rear , under seat. It causes a greenhouse effect. Moisture tries to evaporate and rises causing drops on windshield. Being an 18 I would bet my life it's not your heater core. You have a slight leak somewhere causing dampness. Use the back of your hand and feel everywhere. It could be such a small leak that you will never find it with a hose or car wash. Once something is damp and you get the greenhouse effect it's a cycle that keeps getting worse because the dampness created just goes on and on.

 

The drain hose to outside through your firewall is from your heater box under your dash. That is where your a/c evaporator is. If the drain is clogged and you're running your a/c, the condensation dripping off your evaporator has no where to go and will collect in the heater box and evaporate eventually. If you're not running your a/c yet then... never mind... not the problem.

 

Turn on the Defroster

 

That was my problem, running the AC would cause condensation to build up on the windshield, also if it was real humid and the windows would be rolled up it would do the same. I would have condensation on the inside almost every morning when I would get in the truck but I live in North Carolina close to the coast so it is humid. Running the fan would soak the floor because of the water build up in the heater box

 

check your cowl vent is not clogged with debris from all the trees/pine needles, etc... they get in there and clog up the vent, and the water finds its way into your airbox, the airbox drain eventually clogs, and as the moisture attempts to evaporate it evaporates into you cab.. eventually you will get a horrid smell in your cab from the mold growing in your cab/airbox.. be sure the cowl vent drain is cleaered, and that debris are cleaered out of the cowl every winter/spring. its also a good idea to change out your cabin filter at this time as well. if you have an inspection camera or access to one ($35 on Amazon)

DEPSTECH Wireless Endoscope, IP67 Waterproof WiFi Borescope Inspection 2.0 Megapixels HD Snake Camera for Android and iOS Smartphone, iPhone, iPad, Samsung -Black(11.5FT)

https://www.amazon.com/DEPSTECH-Waterproof-Inspection-Megapixels-Smartphone/dp/B01MYTHWK4/ref=sr_1_3?crid=3H5C2IYFPHFJW&dchild=1&keywords=inspection+camera&qid=1586362368&sprefix=inspection+cam%2Caps%2C180&sr=8-3

you can look into the airbox via the cowl vent, and the filter access. check for debris, and mold. they are a worthwhile tool to have.. but try to get a shorter one 16ft is super long (I have one this long, and is a bit large/cumbersome with all that cable.... they are also useful for inspecting intake/bores and hard to reach areas.

others areas to check are if you have a roof rack, check the headliner, and also check under the flooring/carpet. if there is standing moisture there you may have other issues (think windshiled sealing, window/door seals/scrapers

 

Yes....sooooooooo, there's a homeless person sleeping in the truck at night. OR, the some teenagers down the street are using your truck as a............................well, nevermind.
Hope you get it fixed.
Zim