toyota highlander drips water under car, regardless of whether a/c is on or not, blow hot air out vent a/c off

Answer 1

Where is the water dripping from it could be a condensation hole in the muffler if it's mid way back under your truck. When a gasoline engine burns gas it creates over a gallon of water for every gallon of gas it uses so the muffler needs a hole to keep water from building up inside. If that's not the case your ac may be staying on. If you are using the defrosters the ac will run to remove moisture from the air therefore your ac will drip. Be sure it is just plain water and not coolant that could be a lot more serious.
as far as the hot air if it is just a little worm it is probably normal all cars have a small amount of air circulation even when the climate control is off. this is to prevent carbon monoxide poisoning in case you have an exhaust leak getting into the vehicle. The air inlet is located in the cowl right below the windshield so engine heat usually heats the air going into the cabin.