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How to best use your car’s HVAC system and save time in the morning

January 17, 2018

How to best use your car's HVAC system

For all of us, there are big questions that remain unanswered for too long. Thankfully, the Internet provides guidance when we need to immediately know the origin of the Twinkie or the health benefits of black tea. But what about the times our phones aren’t accessible for a quick search – namely, these cold winter mornings when we’re behind the wheel, late for work and can’t see out the windshield?

Fear not! We have your car heating questions answered, so you don’t have to suffer through any more half-defrosted windows when you’re already behind schedule. To protect you and everyone else on the road, we compiled all the tips in one place, so you can read them safely in the comfort of your home. Enjoy.

The fastest way your HVAC can defrost your windows and the science behind it

We investigated nearly every possible scenario to properly address this question, and found the answer in science. To defrost your windows most quickly, use both your car heater and a DIY melting spray.

First, your heater settings. You’ll want to do four things:

  • Turn climate control to the hottest setting
  • Turn on the A/C
  • Make sure recirculation is disabled
  • Turn fan to full blast

We know, three of those four make complete sense. But why would we turn on the A/C? Well, the trick is to remove excess moisture from inside the car so that the windows don’t fog up as they’re warming. That moisture will just freeze again or cloud your view as you’re driving. Warm air can hold more moisture than cold air, so we want to get things warm as quickly as possible. And our cars’ A/C systems run air through an evaporator that removes moisture as it passes through, ensuring that we’re bringing the driest air possible through our vents.

Next, we use some science to quickly get the ice off the outside. The recipe for our melting spray is a simple mix of two ingredients — 1 part water to 2 parts rubbing alcohol. Put the mixture in a spray bottle and have it ready for the next cold morning. Alcohol has a freezing temperature of -128 degrees Fahrenheit, so when it comes into contact with ice, it immediately begins to melt it.

Combine those two methods and you’ll be ice-free in no time at all.

What that recirculation button really does

Only use your recirculation button in the winter if you want your windows to fog up inside the car. The recirculation setting is really meant for summertime, to save your A/C from having to cool hot summer air. Recirculating air in the winter also recirculates moisture from you and your passengers, trapping humidity inside of the car. As we learned above, cold air can hold less moisture than warm air, so we end up with lots of fog.

Save recirculation for the summer.

Save gas and skip “warming your engine”

If your car was built in the last couple decades, its engine is ready to run after about a minute of running, even on the coldest days. Let it idle beyond that, and you’re wasting fuel. In the days of carbureted engines, running them for 10 minutes prevented stalling, but today’s cars don’t need to wait.

A best practice is to let it run for as long as it takes to scrape any ice off the windows – no more than 5 minutes – and then start driving slowly (slamming on the gas will add wear to the engine). Cars actually warm faster when they’re being driven, rather than running idle. After 5 to 15 minutes of normal driving, your engine will be warm.

The future is looking warm

Automotive climate control systems are getting more advanced every year. Teslas today can even be warmed in advance using an app. But until everything is electronically controlled, it’s helpful to know how to use your car’s HVAC to save fuel and time.

 

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