Dew point, that's when the moisture inside your car turns to condensation. Whether the fog is on the inside of your window or the outside, it can really create a safety hazard! Fall is in the air and cooler weather outside is more likely to cause fog to form on the inside of your car windows. It has definitely happened to all of us, you're running late, you hop in your car, fire the engine up, and look up only to find your windshield is way too thick with fog to drive safely. Somehow you've gotta get moving, 5 minutes ago! Thankfully you can turn your defroster on and let your car take care of the rest. If that's not working for you, definitely take your car in and have the AC checked! Did you know that your defroster uses your air conditioning system to quickly wick away all that moisture? Your air conditioner (whether your heat is set to hot or cold) is designed to condense the moisture out of the air into water, then the condensation is vented through a drain hose under your car. Your defrost, whether you are using the heating or cooling system is designed to remove the moist air in your car and replace it with dry air, pumping it towards the windshield clearing your line of sight. If you're in a huge rush, lower your temperature and crack a window, don't turn on the heat! quickly lowering the temperature will help reduce the fog. Unfortunately, this will obviously leave you shivering! Be sure to turn off the recirculate option, if you're not sure how to do that, just look for the button that has arrows pointing at each other in a circle. The reason you don't want to have air recirculating is because your objective is to remove the moist air from inside the cab and replace it with dry air from outside.
If you're short on money right now and need another solution, be sure to try a silica gel absorbent. While there are lots of DIY hacks, if life hacks have failed you in the past, you can always make a trip to the hardware store or Walmart and get moisture absorbing desiccant. Here's a link to an inexpensive variety, don't expect overnight results, and remember, with wet feet constantly in and out of your car, your best bet is to save and fix your air conditioning system.