Question: Is there any way to defog my car windows if I don’t have A/C? My A/C is broken but I need to drive my car every day – whether it’s raining, freezing or hot and humid out.
Answer: Driving with fogged windows and windshields is dangerous, but fixing an A/C is expensive and a parts shortage might cause repair delays.
The good news is you don’t need to use the air conditioner to defog your windows. The basic principles behind reducing windows that have fogged up include:
- Reducing the humidity in your car
- Getting this dehumidified air flowing across your windshield and windows
Defogging car windows without A/C
On a cold day:
- Max out the heat
- Turn off internal circulation (i.e., draw air from the outside)
- Crack the windows open
- Use the defrost mode (look for an icon with a window and hot air streaks)
If you have a working A/C, you should turn it on, but you’ll slowly see progress even if you don’t.
You might see little progress initially because your engine might still be cold. Once your car gets up to temperature, hot air will flow, and your foggy windows will slowly clear up, even if you don’t have air conditioning. Light driving, if safe, can speed up the warming up of the engine.
Let’s discuss theory. Hot air can contain more moisture than colder air. So, heated air will speed up the evaporation of water droplets that have condensed on your windshield. Cold air that has not been dehumidified, might not be able to absorb much more water vapor.
So why do we recommend using the A/C if yours is working? Why do some cars with automated climate control turn on the A/C when you press on the defrost mode?
That’s because an A/C has a dehumidifying function. Every time an A/C cools air, it also dehumidifies the air to a small extent. If you are going all out and trying to defog your windows, this can help speed things up.
On the other hand, you might also encounter foggy windows on a hot summer day, especially if you live in a humid, coastal state like Mississippi or Florida. Unfortunately, dealing with fog also requires the same technique—blasting the heat, turning off internal circulation and using the defrost mode to direct air to the windows. If you have working A/C in your car, turn it on.
It can become unbearable to defog your windows this way when it’s already extremely hot outside. The only way to reduce this is by cracking your windows so cooler air can come in.
You can also undertake some of these preventative measures:
- Keep your glass clean. Dirt attracts moisture and regular cleaning to remove dirt, dust and fingerprints can reduce the moisture on your windows.
- Use desiccants or cat litter to prevent moisture from absorbing moisture. Reducing the humidity in your car will reduce the chance of windows fogging up.
- Use an anti-fog spray like Rain-X. These products create a hydrophobic surface that causes water to bead up and run off surfaces.
Xuyun Zeng is a content strategist with a wide-ranging content background including tech, journalism, cars and health care. After graduating with highest honors in journalism, Xuyun led a newspaper to win eight awards, helped start an award-winning film industry podcast and has written over a hundred articles about cars repair, state laws and insurance. Prior to joining Jerry, Xuyun worked as a freelance SEO consultant with a mission to create the best content that will help readers and grow organic traffic.
Giselle Gomez is an editor with over a decade of experience editing content across personal finance, education, travel, and sports. In editing for Jerry, Giselle’s focus is on making sure content is consumer and SEO-friendly and helping readers understand all things car ownership. In prior roles, she worked as a content strategist, syndication editor, and writer. Her work is featured in AP, NerdWallet.com, BestColleges.com, and more. Giselle holds a master’s degree from Arizona State University.
