Temperature control knobs in cars

Does anyone ever use the temperature control knob in their cars while they have the A/C turned on? I don’t. It seems to me, that it is inefficient to have the A/C (compressor) turned on to cool the air, and then using the temperature control to add heat to the air your compressor just cooled. The only time I ever use the temp control knob is when its cold and I want the heat on, in which case the A/C compressor is turned off and no energy is being wasted.

I’ve seen people who leave their A/C turned on ALL the time and have the temperature control adjusted (towards the red) in order to not have the air come out too cold. I, on the other hand, have a car whose A/C is like ice at the coldest setting. So I leave the temperature control at the coolest (all blue) setting, and when it gets cold I simply turn off the A/C (compressor) and keep it in recycle mode (so that the cold air is recirculated.) Then, after a while, I’ll turn the A/C back on until its thouroughly cooled again. This seems to me to be the most efficient way of doing things, although some may argue that by turning on and off the compressor more often, I am causing it more stress. I say that leaving it on ALL the time would be even more so. Furthermore, this has long since been my MO, and I have definitely had far less (none) problems with my various cars cooling systems compared to my aquaintances. Add to the equation slightly better gas mileage, and I think that makes it downright wasteful to use the temperature control to heat your cooled air.

I know, I’ve said a lot so far without posing any real questions, so here it is:
Why, in this era of high gas prices and hightened concered over energy conservation, don’t car manufacturers put actual thermostat controls in cars air conditioning systems? The way I see it, there HAS to be a good reason to waste all the energy.

If you still don’t get what I mean, think of how your home’s air-conditioning functions as opposed to your car’s air-conditioning.

Actually when you defrost your windows they suggest you turn the A/C on with hot air because the A/C takes humidity out of the air, supposedly making the vehicle defrost faster. Other than that though I agree with you that usually you don’t need to have your A/C running full time.

Well, that is true to an extent. The A/C being on does take the humidity out of the air. Although the temperature should be adjusted either up or down in order to approximate the temperature of the outside air. This is why if you start out with a window frosted on the inside, and you turn on the defroster with the A/C on and turned to cold air, it WILL defrost the inside of the window. But then, it will begin to frost the outside of the window because of the temperature differential between the inside and the outside.

anyone else ever wonder why they don’t use an actual temperature setting (like in house thermostats) i mean that way, when you got a new car, you would be able to find the right setting easier (i guess what ever you have in your house)


I believe Cadillac does have an actual temp. setting for each individual front seat passenger.

A number cars have a temp control that lets you set the temperature. My 86 Taurus, 94 Grand Marquis, and my 99 Honda Accord for example. The Honda has a pretty neat controller that uses fuzzy logic to decide whether the air is recirculated, fan speed, and which vents are open
The older AC’s used about 7 horsepower, but the newer ones are more efficient and use somewhat less. I don’t remember the exact number, but 3 to 4 horsepower is what I recall. In any case I would be surprised if you see much increase in fuel efficiency by manually turning the AC on and off.
One thing I have read is that it actually uses more fuel to drive with the windows open (at highway speeds) than it does to use the AC. The open windows cause increased air resistance that wastes fuel

My 98 Volvo has a temp control for each of the front seats. Also, the manufacturer advises that you leave the blower on all the time and that you always use outside air instead of recirculated air. You have the option of turning on or off the A/C and regulating the temperature.

Believe it or not, all of this is supposedly designed to make the car run better and more efficiently.

After moving to Virginia, I found out that A/C is a must. Besides blessed relief in the summer, it helps defog windows in cooler weather.

(I grew up in the desert part of Colorado [not shown in the tourist pamphlets], where plain hot air was enough for defogging.)

I do try to use the A/C as little as possible, but sometimes even breath-exhaust makes the windows fogged up enough to have to use the A/C.

My summer mileage was about 32 mpg (13.6 km/l); overall mileage is 33 (14). So using the A/C for me is economically feasable.

Living in Atlanta I use mine for dehumidification a lot. Turning it on full is too cold and turning it off is too damp. I’ve found that adjusting the temperature gauge is a good way to stay comfortable.

“Drink your coffee! Remember, there are people sleeping in China.”

Dennis Matheson — dennis@mountaindiver.com
Hike, Dive, Ski, Climb — www.mountaindiver.com