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Economical air conditioning usage?

I have a 2005 nissan altima, a 2008 honda ridgeline and a 2010 toyota venza. Recently I got the idea to run the air conditioner on max cool until it gets too cold, then turn the air conditioner off until it gets hot in the car. I am wondering if this is harmful to the compressor? I also assume that when the air conditioner is on, the compressor is always running, no matter where the temperature is set. Is this correct?

Yes, the compressor runs constantly when the A/C is turned on, no matter what temperature you select.

Others may differ with me on this issue, but–IMHO–you will be accelerating the wear and tear on the compressor clutch by turning the A/C on and off the way that you described. As a result, I think that you will not save money in the long run, and may actually wind up paying more money for repairs than the miniscule amount that you would save on gasoline.

And, then there is the discomfort factor.
Do you really want to be uncomfortably cold and then uncomfortably hot for much of the time that you are behind the wheel, just to save–literally–a few cents?

If discomfort isn’t and issue, just open the windows and leave the AC off.
Otherwise, I agree with VDC. You’'re better to just set it and let it run.

Just turn on the a/c and forget it. Any gain in fuel economy will be meaningless. The compressor cycles on and off on its own anyway depending on the demand on the a/c system. Do you run your home furnace/air this way to save electricity?

Whether you know it or not your a/c compressor is running all winter when you have the defroster or heat/defrost blend on.

“Do you run your home furnace/air this way to save electricity?”

We just don’t run our air conditioner at home unless it is in the 90s with high humidity. When we were younger, we never, ever ran the AC - even when it was over 100. But back then, we had a lovely 28,000 gallon in ground pool (installed by a previous owner) to cool off in. When we went upstairs at 10 or 11, the top level had cooled considerably. I’m too cheap to pay for such a luxury at the new house. And I don’t miss cleaning it either.

The amount of money you’ll save here is very small. I know that I’d never trade my comfort for that amount of money.

Do you keep your car properly maintained with the proper tire pressure? Can you figure out a way to avoid a few trips per month by combining errands? You’ll save more money that way than by worrying about the air conditioning.

It is very possible that turning the A/C off and opening the windows may reduce your mileage.  Open windows generally increase the drag and reduce the mileage.   It may not amount to much, but I doubt if you are saving anywhere close to enough to get me to play the game of not using the A/C to maybe save money.

I have had two vehicles with automatic temperature control–a 1993 Oldsmobile 88 and our present 2003 Toyota 4Runner. I have experimented and manually overriden the automatic temperature control and could see no difference in the fuel economy. My recommendation in the car is to set the air conditioning where you are comfortable. I think being comfortable makes a person a safer driver.
When I start out in a car that has been sitting in the hot sun, I lower the rear windows with the air conditioning blower on high to expell the hot air and drive this way for a couple of blocks.
I do something similar in my house. I have an attic fan that draws air out of the house and exhausts the air through the roof vents. I run the fan before starting the air conditioner to force the hot air out of the attic. I’ve also found that if it is cooler at night that I can open some of the house windows and run the fan and not the air conditioner. In the morning, we turn off the fan and close the windows. I’ll often not have to start the air conditioner until the afternoon.

Turning off the AC in your home and moving some outside air, may work very well in some environments but not all. It gets a little tricky when you need to add in humidity.

Yes, the compressor runs constantly when the A/C is turned on, no matter what temperature you select.

VDCdriver: What were you trying to say here?

“What were you trying to say here?”

What am I trying to say? I am responding to the question that the OP posed in the last sentences of his post. In case you did not bother to read to the end of the OP’s post, this is what he wrote:
I also assume that when the air conditioner is on, the compressor is always running, no matter where the temperature is set. Is this correct?

In order to expand on what I posted, I will add that, years ago, A/C compressors cycled on and off in order to regulate the desired temperature, but on all modern cars with which I am familiar, the compressor runs full-time when the A/C is turned on, and the temperature of the conditioned air is regulated by blend doors that blend chilled air with heated air.

VDC:
The way your comment was worded, it sounded like it was universally true.
It is true for variable displacement compressors, which the industry has moved to in recent years.

I wonder if any new cars still use fixed displacement compressors, or have they all switched over.

VDCdriver I have had air-conditioned cars since 1965 and on all of them the A/C ran all the time it was turned on. However, automatic climate control may operate differently, I don’t know. It seems to me that if the A/C cycled on and off that the clutch would not last long.

I wonder if any new cars still use fixed displacement compressors, or have they all switched over

@JoeMario: can you give a rough idea when this transition occurred? Thanks.

I was hoping someone more familiar with the transition would comment.
I thought the transition occurred in the mid-to-late 90’s.

I don’t understand EllyEllis’ reply, since I didn’t think variable displacement A/C compressors existed for cars in 1965 or even for many years after.

Thanks JoeMario.

Running the A/C incurs about a 5%-10% mileage hit (or up to 35c a gallon cost with today’s prices). MAX A/C can incur a 10% to 15% mileage reduction.

  1. Window tint, with infrared blocking properties help keep the car cooler as it sits. If no rain forecasted or in a safe area, keep the side windows and sunroof cracked open a bit to keep the interior cooler than if all windows closed. Park it in a garage, under a shaded tree or under a carport if possible.
  2. Once you enter a hot car, roll down the windows to blow out the hotter air as you drive a bit, while running the A/C to get the evaporator cold. Roll up the windows in a minute or two once the hot air is out.
  3. “Recirculate” the air, so the compressor works less to cool the same interior air. If the window fogs, take it out of recirculate for a period of time.
  4. If you are trying to maximize mileage (this takes some thought and effort), then run the A/C compressor on downhill segments and turn off the compressor for uphill segments (keep the fan blower running, though). Keep the recirculate selected so as to keep the cool air inside the car as long as possible. When it gets a bit stuffy, turn on the compressor again.
  5. Set the temp selector to 76F (nstead of MAX). 76F will feel cool after a time, especially as the humidity is taken out.
  6. Point the vents directly at your arms and bare skin for maximum cooling sensation.
  7. In the Summer during early mornings before the heat builds, you can just roll down the window a few inches on one side of the car, and get a nice interior recirculation pattern going that feels nice without running the A/C at all. Works even down here in Florida if the humidity is not too bad, and the sun is not into the car (overcast).
  8. Remember “MAX” will run the compressor FULL TIME, and really eats into the mileage (15% hit on mileage… or 60cents a gallon!)
  9. From my own experimental runs, having the windows down six inches does not affect the mileage anywhere near running an A/C compressor. From my instant MPG readout, there is no effect at all on my car. But the compressor robs about 10% mileage when it’s engages (half the time or so as it cycles on/off).

These work for me to maximize my mileage (I average about 65mpg on the interstate, even in the Summer…and stay comfortable with the above techniques. Of course, I blow it on MAX at times, if I’ve been working in the yard and hot & sweaty and my core temp is up a lot. Just depends…

Good luck!

Doc Rings

“I don’t understand EllyEllis’ reply, since I didn’t think variable displacement A/C compressors existed for cars in 1965 or even for many years after.”

Yeah, I was really confused by that comment also. I know that none of my cars had variable displacement compressors in the '60s, or the '70s, and maybe not even in the '80s.

As Joe Mario suggested, I think that this feature did not begin to become commonplace until sometime in the '90s.

Joe, Chrysler used variable displacement compressors on 1990-1992 3.3/3.8 Liter C/Y bodys and mini vans. I believe some imports use a variable displacement compressor at that time but not many.
The Caliber/Compass/Patriot uses a clutchless compressor, the compressor is always turning when the engine is running. The compressor uses pressure to adjust the wobble plate like the older units. The wobble plate is in the straight or neutral position until the unit is turned on (A/C request from the PCM). All other Chrysler products cycle the clutch.

These are the only ones that I am familiar with. I have been working on Lexus vehicles for the last 3 years and all exept hybrid cycle the clutch to control pressure.

Thanks Nevada.
I also just found this in an SAE Engineering article discussing the “then new” 2011 Ford Explorer:

The midsize Explorer gets the automaker’s first North American application of a
variable-displacement air-conditioning compressor.

http://www.sae.org/mags/sve/8609/

I would have thought Ford switched long ago.