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Originally Posted by ps2fixer
The way AC works, it has to pump the refrigerant and do phase change and such. So initial turn on it has to work harder to cool, besides the extra heat load of the car being warmer as well. Kind of like cold starting an engine. Once it's ran for a while, it should take less for it to catch up. I didn't think the numbers would be so wildly different though.
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Part of the wild variance is that as the interior cooled I reduced the fan speed which then put less load on the A/C system. With the fan on max, A/C wattage dropped from 2000 to maybe 1400 or so before I started getting cold. It may have continued to decline more if I'd wanted to stay in an icebox...
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But the hottest day I've seen so far was around 88F and windows cracked 3-4in was fine for me.
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I'm windows down till about 45 mph. If outside temperatures are below 75, I just roll the windows up and use fresh air vent with the fan on.
Windows down 3-4 inches keeps me cool enough below 90F, but I have to crank up the volume to listen to an audiobook or podcast and that noise fatigues me by the end of the day. Headphones would solve it, but they're illegal to wear while driving here.
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I haven't done much AC tested with my car, but the little I've messed with it, it really hurt my mpg.
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Yeah, it really hurts the slower go. Looking at the power required to maintain speed according to the ecomodder calculator:
30mph: 2.9kW (750W A/C would require 26% more power)
35mph: 3.6kW (750W A/C would require 21% more power)
40mph: 4.5kW (A/C adds 17%)
45mph: 5.6kW (A/C adds 13%)
50mph: 6.8kW (A/C adds 11%)
55mph: 8.3kW (A/C adds 9%)
60mph: 10.1kW (A/C adds 7.5%)
65mph: 12.1kW (+6%)
70mph: 14.4kW (+5%)
75mph: 17.0kW (+4.5%)
80mph: 20.0kW (+3.8%)