By Elvis L. Hoffpauir, MACS president and COO
Chances are, if you take any kind of extended road trip over the hot summer months, you’re going to see this sight: two feet sticking out of the passenger side window, legs crossed at the ankle, as a vehicle cruises down the Interstate. Perhaps it’s an expression of freedom or rebellion, a penchant for the sensation of bugs striking flesh at 65 mph or so, or one person’s vote in the years-old debate of which yields better mileage – windows down, A/C off or windows up, A/C on.
Back in 1979 when I first became involved in the mobile A/C industry, I was working for IMACA (the International Mobile Air Conditioning Association), which had just mounted a PR campaign to convince motorists that the use of mobile air conditioning was not only beneficial, but more fuel efficient than blasting down the highway with the windows rolled down. That year, the debate was perhaps more important than most years, because it marked the second oil crisis in the wake of the Iranian Revolution (the first crisis occurred in 1973). High prices and long lines at the pump sharpened the focus on fuel efficiency.
Over the years, many have weighed in on the question, including the folks at Discovery Channel’s MythBusters, who tackled the issue twice, coming to opposite conclusions each time. This isn’t necessarily surprising, because a host of variables come into play in any such comparison – variables not easily controlled.
As MACS technical consultant Ward Atkinson observes, “The energy required to provide comfort in a vehicle depends on many factors. The load on the A/C system is a function of the fan setting, the weather conditions, outside temperature and humidity, and the speed of the vehicle among other variables.”
Atkinson further notes, “Since the user has many options in operating the A/C system, it is important to have an understanding of the effect of various settings on fuel consumption. The use of recirculated air and reduced fan speed result in the lowest energy requirements. However, the use of outside air and a selected fan speed will provide a more desirable air exchange and air quality within the passenger cabin.”
Given that many motorists’ knowledge of their A/C systems may not extend beyond turning the systems on or off, a brief tutorial for your customers may be worth your (and their) time.
Much information available in print or on the Internet tells only part of the story. For more detail on this subject (including suggested A/C settings for energy efficiency for various driving and weather conditions), check out the paper by Ward Atkinson and Bill Hill on “Mobile A/C system energy requirements.”