Do colder A/C temperatures use more gas?

airconditioning

#1

In a 2006 Scion, if I set my climate control for the A/C to a very cold setting, would it make the compressor work harder, and the use more gas, or does it not matter what the temp is set and the compressor would be working just as hard?


#2

The system has a set amount of freon, say about 1.5 - 2 lbs in this system. When the compressor operates it will always circulate the same amount. When you set the temp lower the compressor will just operate in longer cycles to achieve the lower temp setting.


#3

Thank you!!!


#4

As Willey said, the colder the temperature setting, the longer the compressor runs. Since it takes energy, which comes from fuel, to run the compressor, maintaining a lower temperature does take more fuel. On the other hand, I don’t think it is worth stewing in your own sweat to save a fraction of a mile per gallon.


#5

Yes it will use more gas. There’s no such thing as a free lunch. You want more regrigeration power, so you must consume more energy to achieve it. However we are talking about a difference of probably less than 1 mpg. Slow your driving speed and you get it all back. It really does not pay to fret over such trivia.


#6

I agree that you will use slightly more fuel because the compressor spends a little more time running.

Note that this is only true for designs where the compressor actually cycles on and off. Some older AC designs (like mine) run the compressor all the time and control temperature with the heat. Not very efficient, but good for removing humidity from the air.


#7

I’l disagree. A house air conditioner compressor will run less depending on temperature, but a car compressor is either on or off and is cycled on and off by the computer without regard to temperature setting.

So it is on full cold all the time and the temp is controled by adding heated air to it to make it warmer. So whether full cold or halfway, the compressor will run the same amount. Same gas mileage either way.


#8

Not true, previous poster. On most automatic climate control systems, the compressor IS cycled on and off in accordance with overall cooling demand.

Humidity and sunlight are also a factor with automatic climate control systems. Higher humidity levels require more effort to cool the air. If the sunlight level is high, it takes more effort to keep the car cool because the sun heats the air back up.

On a day when the temps are above 90?F, and the sunlight is full on beating down, expect to see no difference in compressor operation because even if you set for 75 instead of 71, a few seconds of off-time for the compressor can get the system way far behind on keeping up with the heat.

And for the record, many manual systems don’t run full time when the A/C is turned on either. On many GM and Ford systems, the compressor is designed to cycle off when the evaporator temp (and consequentially pressure) reaches a certain low point. If the demand on the system is lower (lower fan speeds, higher temperature dial/lever selection), the evaporator will cool down quicker, and the compressor will cycle out sooner and more often. And I know of some non-cycling systems that will stop compressor use when the cabin gets cold enough, depending on temp dial/lever setting, and especially if in ECON mode.

-Matt


#9

You are correct, it depends on the specific system design. I suspect a new sion will cycle the compressor in the interest of fuel economy.

The climate control system in my 80s cars always runs the compressor (even in heat mode) for dehumidification. The only time they shut off is in ECON mode or when the evaporator temperature gets low enough to cause icing (only in winter). I prefer the old system (if you don’t care about economy) because it doesn’t cycle the compressor as much. I also think having “full time” dehumidification is worth a couple of mpg. I don’t know if any “modern” systems operate like that.


#10

I have rewired the compressor controls on my 1990 to eliminate the relays and the ECU controls. I asbolutely CAN NOT STAND the GM cycling clutch design. Every time the compressor turns on its as if I very quickly tapped the brakes. It’s annoying and not very attractive to passengers either, especially on a long drive on the highway when the clutch is cycling constantly.

Now, I have a little red button on the center trim. I flip it to ON, and the compressor goes on and stays on until I turn it OFF. Neither the computer or the cycling switch can do anything about it. Although the computer does use thermal sensors in the A/C lines to monitor system condition, and will warn me (by putting the climate control system into econ mode, and lighting a light on the dash… which is currently burned out) if the system is not operating correctly.

It’s actually a GREAT setup. The climate control still automatically sets fan speed and heater blend, and vent selection, I just have direct control over the compressor.

Yeeah this is somewhat off topic, sorry. Had to vent about stupid cycling clutch systems though. Why doesn’t GM just use an expansion valve? >=-/

-Matt