Setting AC to Medium position waste Gasoline?

Just wondering how the AC in Vehicles work. When you set the Air conditioning to less the max, does The AC still work at maximum capacity while mixing the really cold air with some hot air?
If so, I would say that there is cold air is being wasted. It would make more sense to me if AC would turn on and off every few minutes, when you have it set to medium cold. As far as I know the AC is either on or off. There is no such thing as partially on. In my house the AC is on max and when the desired temperature is reached, the AC turns off. Can someone clarify this to me? Thanks.
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Actually you are closer to the truth than you may know. The AC in your car doesn't work full time, only the fan does. The AC compressor under the hood has a clutch mechanism that engages and disengages the compressor whenever it's needed or not. The amount of power the fan uses by having it run constantly is negligable on the low and moderate speeds so it doesn't make economic sense to add in a switch to turn off the fan while the AC compressor is disengaged. In fact, I think the interior of your vehicle would heat up faster if the fan wasn't running anyway, so you might as well keep air moving over the coils which are still cool after the compressor shuts off. Putting the controls on Max or Hi doesn't effect the compressor, just the fan speed and recirculation vent. It's actually more efficient to run your AC on "Recirc" where it draws in the already cool air from inside the passenger cabin, and many vehicles these days have a dedicated recirc button that can be activated regardless of fan speed.
Hope this helps.
Cheers - Jonathan

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On not so newer GMs, before GM decided to use a "recirc" button like the rest of the world, the "recirc" function is the "max" setting on the dial.
Steve
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Even back in the 1960's the GM AC systems used the "Max" terminology for the "recirc." function. I hadn't realized they finally changed it to the term every one else uses. Interesting.
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My favorite is the "Desert only" setting on Rambler air conditioning.
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On Wed, 15 Jun 2005 18:47:30 GMT, "Jonathan Race"

But don't run Recirc when temp outside is below freezing. What happens then is the moisture from your breath accumulates in the air and, when you turn off the motor, becomes ice on the interior of the window a
Then the next time you run your vehicle the ice from the windows gets into the air and it's a vicuous cycle. F
I've seen any number of vehicles over the years where the windows are frosted up all the way around due to this problem.
Tony
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Many home AC system have a feature that shuts down the blower, as well as the compressor, when the desired temperature is reached. The HVAC systems in automobiles do not, generally, have that feature. That does not mean they do not shut down however. The blower in AUTOMATIC climate control system will cut back but, generally, does not shut down. The compressor on both manually and automatic operated systems in cars does shut down when the desired temperature is reached, then restarts as needed. Generally, in cars the MAX setting is NOT the temperature setting, it is simply used to operate the AC in the most efficient mode by re-cooling the dehumidified inside air, much as it does in a home AC system. If not set to the MAX setting the system, generally, is taking in outside air and cooling that air. When using outside air the compressor operate more frequently to maintain the same temperature setting because it must cool the warmer more humid outside air than if inside air is the source of the air being cooled.
mike hunt
snipped-for-privacy@yahoo.com wrote:

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Every car I've ever seen does not cycle the Compressor on and off to control temperature, it does how ever throttle down the blower to lower the amount of air passing over the cooling side of the coils.
try www.howstuffworks.com for a breakdown on how A/C works in general.
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Then you're seeing old GM cars with a suction throttling valve. Some cars also had thermostatically controlled expansion valves. The newer cars cycle the compressor to hold the evaporator temperature just above freezing.
Al
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You have not seen many cars, apparently. LOL
mike hunt
Paradox wrote:

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wrote:

Then explain why in my 88 Olds the magnetic clutch engaging and disengaging when the A/C compressor cycled on and off was dimming my headlights when my alternator was only putting out 30 amps.
Tony
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Every car I've owned cycled the compressor. I've not owned any that changed cabin blower/fan speed automatically.
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AMC cars vary the compressor cycle to control outlet temperatue. Probably there are others that do as well.
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On 15 Jun 2005 11:36:32 -0700, snipped-for-privacy@yahoo.com wrote:

You are correct, the way it's done now is somewhat inefficient and is different then how it's done in your house. In the "old" days the AC in cars did have a temperature control similar to your house that ran the compressor all the time until the temp was lowered to your desired temp and then it shut it off till the temp went back up. But because your car has so much more window and heat load then your house, it was very hard to maintain the temp within any reasonable degree of fluctuation, you were always fiddling with the temp knob. A typical car AC has the same cooling capacity as the home AC for a 1600 sf house. To better minimize temperature fluctuations in the car, modern AC basically runs at max compressor output all the time and simply cycles the compressor off whenever the evaporator coil temp gets low enough that there is a possibility of freezing of the condensed water. (In the old days they would literally blow ice at you if you set the temp control all the way down). The current way to control temp is to change fan speed and/or move the temp lever so some of the cold air gets reheated by running it thru the heater core. Of course there are tons of variations on these themes with all sorts of combinations having been tried over the years by cycling compressors by temp, by pressure, and running them constantly but changing how the freon flow was metered, how the heater core was operated (water valve vs diverter door), size of components, temperature of components, etc. Presumably, what we currently have is what evolved as "best" since it seems all the makers have pretty much adopted the same basic system operation now. One major benefit of the current, slightly less efficient operation, is that it maximizes the amount of humidity that gets removed from the air since the ac is always "on" in the sense that the evap coil is run as close to freezing as possible without giving you a headache or actually freezing up. That's another change from the old days, they used to run the coil so cold the air blowing on you was like a walk in freezer, now they seem to keep it a little higher so it's not giving you an ice cream headache. There are lots of variables they can play with....
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