Heavy condensation inside headlight on my 01 toyota highlander

Warm moist air inside condenses on the colder windshield,

1Lower any greater moisture than outside by turning the recirculate control to fresh air setting

2Warm with fan defrost which also turns on AC most cars to help remove moisture

3 clean well, all dirt not always visible

https://windowtintlaws.us/condensation-on-the-inside-of-car-windows/

Ricart Automotive Group Why Does Water or Moisture get Inside my Headlight
This link may be helpful ...
If the wetness is bad ... it usually means there is a seal problem somewhere ... especially if the problem shows up after driving a lot in the rain.

Use a hair dryer from the outside or leave the headlights on to dry out the moisture. Check the lens assembly for any cracks allowing water in.

Yes, the cartridge is on the side of the condenser. It can be replaced without replacing the condenser. The expansion valve is on the firewall where the lines go to the evaporator.

First, if there is water in the lens, then it is leaking. The best way is to get the lens in a dry environment, like an air conditioned house, remove all the bulbs. Use something like a hair dryer to help the moisture evaporate. Next you need to seal any leaks. New aftermarket lenses are available for a reasonable price on line.

We'll if you are replacing bulbs and they work when you put them in but burn out quickly, that symptom along with condensation inside the lens surly indicates a moisture problem meaning somewhere there is a bad seal in the headlight lens assembly.

I changed my 2001 Toyota Highlander headlights recently. First, remove the grille. There is one screw in the center which will require a loonng Phillips screwdriver to reach it, down behind the grille, right in the center. Then remove the four plastic clips at the top by prying them up with a small flathead screwdriver. The bottom just pulls forward. Important: Now go to each side of the car, and in front of each fender well, there is one clip that holds the bumper cover on. Pull the top corner of the bumper cover toward you to release the clips, one on each side, at the top corner, along the front of each fender well where the bumper cover meets the fender. The bumper cover can now be loosened along the top without entirely removing it. It just pulls forward. Inspect the underside of the bumper cover for broken clips and replace as necessary. Now remove the two bolts that hold down each headlight at the top. Disconnect the wiring and bulbs and wiggle the old headlights out. Install the new ones and reverse the process. If your AC isn't blowing cold, check the condenser for leaks before you reinstall the grille. A new aftermarket condenser/filter dryer is easy to install by removing the battery and tilting the radiator back to get the condenser out. A replacement only costs $75 and can be swapped out in one half hour with a few metric sockets. Then you will need to recharge the AC system with R-134a, which is easy. Just buy a R-134a kit with hose at Autozone and follow the directions. $50 Replacement fog lights are only $52/pair for aftermarket. You may consider replacing those as well. They have a strange installation with clips and you will need to pry/bop them forward, not remove them from the back. They are aggravating to replace but not technically difficult.

{: ) Some exterior lamps, such as cornering, turn signal, backup, headlamps or tail lamps may exhibit very small droplets of water, a fine mist or white fog (condensation) on the inside of the lamp lens. This may be more noticeable on lamps with "multi-lens" designs and may be normal during certain weather conditions. Condensation occurs when the air inside the lamp assembly, through atmospheric changes, reaches the "dew point". When this takes place, the moisture in the air within the lamp assembly condenses, creating a fine mist or white fog on the inside surface of the lamp lens.
Most exterior lamps on General Motors vehicles use a vented design and feature a replaceable bulb assembly. They are designed to remove any accumulated moisture vapor by expelling it through a vent system. The vent system operates at all times, however, it is most effective when the lamps are ON or when the vehicle is in motion. Depending on the size, shape and location of the lamp on the vehicle, and the atmospheric conditions occurring, the amount of time required to clear the lamp may vary from 2 to 6 hours.
Completely sealed headlamp assemblies (sealed beams) are still used on a limited number of models being manufactured today. These lamps require the replacement of the complete lamp assembly if a bulb filament burns out.

If moisture or droplets appear after being exposed to rain or washing, you can try putting some weather seals on the edges where you think the seal is poor. Check also the headlamp caps. In any case, if the moisture doesn't clear no matter what drying approaches, better replace the assembly.
The bulbs won't cause the moisture, but it is possible that an accumulated moisture on the bulb itself can disable it, although rare.

seal it with some clear silcolone.

the condensate drain is plugged, pull the blower motor out and clean the drain, u will find it full of leaves.