It's over 30°C outside so we want some cool air. I set the air conditioner thermostat to 27°C and feel the cool breeze almost immediately. My wife grabs the dial and winds it down to 19°C. I use the steering wheel buttons to dial it back up and we fight like kids... My theory: the system cools till the interior temperature reaches the target set. Maybe even cools more gradually, taking longer perhaps but using less energy. Wife's theory: cooling system has a fixed output temperature, and setting a higher target is less efficient because it achieves the higher temperature by mixing outside air with cooled air. So who's right? Neither of us?
I only set it to low when it's a scorcher of a day or the car has sat in the sun to long and it's a sauna inside. Sure it might use more fuel but the comfort of me and my baby in the back is more important then that little bit of fuel.
when I first get in the car on hot summer days, I'd set it to low, but once I know I'm comfortable, I'll turn it to 70 or so, less work for the car and probably a middle-ground for nice cool comfort for most human beings And yes, the car most likely has a cabin temperature gauge hidden somewhere (since in winter, it knows when to kick the heaters until the cabin reaches the set 65 or so before the air out the vents start to cool down from the hot/warm it was when car first starts up). I also tell my wife to not turn the dial beyond what is needed (below 70 or so for summer and above 65 for winter), since people should have (hopefully) in the first place worn clothes according to the weather. Light or less layers for summer and layers and coats for winter, so no point going to the extreme cold in a car then hopping out to the heat or getting the cabin super warm then jumping out to freezing temps (it's just not efficient for the car and not very healthy for the human body to keep changing temperature extremes)
In my car, I make all the decisions as to air (amount of), A/C (amount of), temperature (setting), windows (which and how much they're open), I ask my passengers if they're OK, and tell them if they don't like my perfect choices, they can always get out and walk! Simple - Q.E.D.
You've posted a really interesting question here. It's got that element of personal conflict, plus it looks as if both you and your wife are trying to ground your positions in technical reality and you would both be satisfied by finding out what the technical answer is. So instead of fighting like kids, you could turn it into a cooperative research question. It is a research question, because either one of you could be right; cars have been built that work both of those ways. My old '84 Bronco II was built exactly the way your wife describes. Your profile doesn't identify your car model but you've posted in the c forum, so assuming it's a c, I believe your system does have: (1) a cabin temperature sensor, (2) maybe an evaporator temperature sensor (check your shop manuals, I'm not sure), (3) a fully variable speed electrically driven compressor, (4) a fully variable speed blower, (5) a thermostatic expansion valve where the liquid line attaches to the evaporator. So, Toyota has worked quite hard at an A/C system that uses the minimum power to achieve the settings you dial in. In other words, you could probably go back to your wife and say "PriusChat says I'm right, nyaaah" but, maritally speaking, you might get greater mileage out of actually not taking my word for it, but making it an opportunity to drop in at techinfo.toyota.com and looking over the New Car Features Manual, which you can both learn interesting things from, and have fun doing that together. (It takes $15 to get in to the service manuals area, but that's a pretty cheap date.) -Chap
This isn't about physics or efficiency. It's a control issue. That's a discussion for a different forum, but my philosophy has always been to pick my battles carefully.
... coupled with "assume good will and honest intentions when possible." I didn't mention that with gadgets like the ScanGauge II, or phone apps like Torque, I think the actual current power consumption of the A/C at any moment is a parameter you can pull up and watch, so you can combine some empirical numbers with the theoretical understanding you'd get from the manual. And, yes, if the underlying issue is really that she would like the car colder than you would, that has to be addressed in a different way. -Chap
Paraphrasing MSantos (patron saint of all things hybrid): Start the AC in Auto, letting the system determine fan speed, and with a relatively high target temperature set. Lower the temperature incrementally, never so much that the fan races, until you get to a comfortable climate, say around 75F or 24C.
I would suggest harmony is more valuable than optimal air conditioning procedure. I'd pretend that I have come to the conclusion that she is right. Then do whatever I want when I drive alone. A somewhat disingenuous approach that pays tribute to promoting harmony. That will keep things cooler than any setting you choose with the air conditioning.
Ok, but isn't that just another form of argument-on-somebody-else's-authority, which already wasn't fully satisfactory to the marital unit in question? -Chap
I set mine to lowest temp possible with minimal fan pressure. Sometimes I don't turn on the fan at all and let the air from outside come in if I'm on the freeway. My wife tend to be the cold one so she just shuts her side of the vents.
What might also help, is a sun shade for your front windshield. I have one, and it has helped tremendously with reducing heat in the car. When I get in, it's noticeably cooler then it use to be. To let the car decide fan speed, set to auto. But the car doesn't have a fixed temperate of cool air coming out, the temp you set is what it comes out at. Set it to low, and it will be the coldest air. Set it to any temp above and you can feel the difference in the air coming out. Try it out, and decide what's the best action to take. Just remember, when proving the wife wrong, don't gloat. You could always say " what you said made sense, so I tested it out, and found that the temperature of the air changes to what we set it out" it doesn't work like our home AC does" That way, she won't think you are not trying to say "I told you so" Hope this helps.
The Prius uses a variable output A/C compressor - and it does actually use different amounts of power depending on system demand. In this case - setting it lower should actually get it to cool down faster. When you're sitting with the A/C on and the engine is not running, windows down and near a wall (reflecting sound to your ears), you can actually hear the A/C compressor changing tones, stepping up and down in output as you spin the dial. The climate control logic also uses a sun load sensor - raises output if there's a lot of heat on the dash.
Not 100% true. The air temp at the vents will vary based on what temp you set, but the A/C compressor and the blower speeds also vary. The system is set to maintain cabin temperature at whatever you set it at, but the system always mixes some outside air into the climate control system, regardless of whether the system is set for cold or hot.
