Observation in heavy traffic this morning.

Now you've got me intrigued - does the Prius have a vacuum booster, or a pressure booster? I never thought about it, but seeing the ICE isn't running all the time, there won't be a continual vacuum.

 

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I believe it uses the ABS pump.

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To each their own, but I don't agree... Driving the Prius without using the A/C is like avoiding using the Headlamps because one wants to conserve electricity and headlamp longevity...

First: The amount of energy to turn an A/C compressor is significantly different than the amount of energy to propel a 3,000+ lb vehicle. Therefore the A/C impact on mileage will be minor, if even perceptible. (Of course, one could conduct a Bob Wilson-esque test with the appropriate measurements, and take this out of the realm of a couple of guys each offering up their own conjecture... )

Second: The Prius utilizes an *electric*, variable speed compressor, and the climate control system has a computer, and various (humidity & temperature) sensors to monitor the interior climate. This means that the amount of energy that is used is carefully matched to what is needed to condition the cabin air. If you make sure to set the Recirc on, the energy demand is reduced further.

Third: (And, again - to each their own) - but I just paid $26k for my shiny new GEN IV. (And others may have paid more for the various tech packages, etc...). If you can afford a new car as expensive as the Prius (a Hyundai Accent, it sure ain't) - then you can probably afford an extra $100/year (maybe??) to comfortably condition the cabin air and make the driving experience a comfortable and pleasurable one. Again, that's a personal choice, and to each their own.

If great Miles Per Gallon really is your goal, you could always leave the engine off and push the car around - that'll really drive MPG up.... but might further impair the comfort and pleasure of the drive.

 

An accumulator which stores pressure built up by a pump. The Sonic actually has one. Not because the engine turns off, but because a turbo has less, um, waste vacuum for the brakes.

 

Actually there is a good reason for minimizing AC usage, getting climatised again to the outside world. This means being out in 80F weather or a sweater in 50F and having an outdoor life. Leaving the 'refrigerated' office, the walk to the car just gives welcome warmth.

Now I'm not sure if the 2016 Prius will roll-down the windows if you hold unlock. My new ride does and that lets the hot-air blast escape. But you also come to appreciate letting the house temperatures float (within the range of 'she who must be obeyed.')

Bob Wilson

 

Our main use of AC is defogging, typically in rain, and even that's infrequent. I've found it to have a significant impact on mpg. Also, steady use makes the car more prone to the mold problem. There's the argument it's good for hybrid battery temps: monitoring those temps with a ScanGauge, I've seen little or no drop in temps. Also, in cool evening driving, easy conditions, the battery likes to get up to around 35C.

The only caveat: you do want to run it periodically, to keep internal oil circulated, avoid seals drying out.

 

Bob,

I agree with your perspective - to the point that one is within one's "comfort" range - whatever that may be. Certainly, if one works in a suit, and is on their way to work in 90 degree weather and 90 percent humidity, it may not be so comfortable to forego the use of air conditioning.

It was within the context of making one uncomfortable for the (potentially perceived) benefit of MPG, that I suggest that the (potentially perceived) MPG benefit may not be so great. And, when it comes to taking subjective suggestions like mine and making them objective, you're an expert - our own "mythbuster", if you will!

Living in New England, I often chose the sweater option, and attempt to allow the house temperatures to float as much as possible, until I find the limits imposed by "she who must be obeyed"...

I notice that you've gone over to the BMW. I've always had a contempt for German cars (having owned a VW, and it being the "preferred" brand of she who must be obeyed. While their engineering is always quite inventive, my personal observation has been that it comes at the expense of reliability and, well, expense... Best of luck! Please keep us posted on your findings...

Eric

PS - yes, the key fob of the GEN IV can be programmed to roll down all 4 windows if held down. However, it doesn't seem to work as smoothly (sometimes it seems to take longer for the car to recognize the fob than others) as one would desire. But it is nice to be able to let the blast of hot air escape...

 

Another benefit of using air conditioning is that it allows cooler air to enter the battery compartment through the vent fan

 

Is this not mitigated by turning air recirculate off? It defaults to the on selection but I usually turn it off due of off-gassing (not me, the car!). 176 miles and so far, so good!

 

Any AC use causes moisture in the air to precipitate on the AC's "radiator" inside the vent system. There's a drain tube that runs this water out and onto the ground, but it's not completely effective.

Turn your AC off sometime and watch the windows steam up over the next few minutes. This'll persist for the next 15 minutes or so.

There's a lot of threads here: people asking what to do to remedy mouldy smelling vent systems.

Go back 20~30 years, AC was much more of a rarity. Look through literature on how to improve mpg: a common refrain is reducing AC usage.

The Prius AC supposedly has less impact on mpg, but in my experience it's still no "free lunch".

 

In high humidity areas, I've never had a problem with mouldy smell - I suspect because there is so much condensate water washing it continually. And the A/C is almost always on.

A/C compressors today are much more efficient than they were - I remember my VW in 1977 & VOLVOs in 1973 and 1980 shudder and noticeably slow when the compressor cut in - they were a 2 cylinder YORK compressor. The next iteration of 5 cylinder compressors were more efficient, and nowdays many are very efficient variable displacement. These days, on my small engined Fiesta, I can only tell that the compressor cuts in if it's idling. I've observed that the A/C makes about 0.1 l/100km difference in economy these days - where, 30 yrs ago it was more like 0.5 l/100km. Where I live, the only other choice would be to put all the windows down, and these days, cars are more aerodynamic and aren't designed to suck in large quantities of air like in the '50s, but the air just buffets around hurting ears more than cooling down.

The moisture in the A/C is from breathing, sweating as well as high humidity in the air. The A/C will dry the air in the car by allowing it to condense on the evaporator and dribble outside. Here in the moist sub-tropics, you get puddles of water under cars when they park as they drain out, and on really humid days, can watch it drip out of the car in front as you drive along. My home A/C, I set on dehumidify mode (it uses a low fan setting) and the outside drain will actually give a continual run of water on humid days.

 

I would think that the dehumidifying action of the AC would counter-act mold growth!

 

Shouldn't there be a drain? Most other cars have such.

 

Yes, of course. But moisture's permeated through all the nooks and crannies, evaporator (?) fins. Moisture doesn't evacuate through that drain like paratroopers outa a plane.

 

I find that when I roll the windows down in my car that it gets dusty inside (possibly pollen). Would letting the "dusty" fresh air in, cause the filter to clog up quicker than if you just circulate the inside air? My plans are to put on window visors to keep rain out when windows are cracked a bit (when parked) and to open the moon roof to let out the heat blast, thus causing less use of the AC. If I ever do get the Prius Three with the ATP.

 

"Mold growth"? I've never had "mold growth". Could you elaborate? Is this Prius specific?

 

Nor have I, and I've had A/C since 1973, lived in the tropics, where humidity can be 90% for days on end.