Learned something on nasioc today
 

Not sure if the same applies to the svx but in my outback when you have the air set to defog it uses the ac to remove moisture on the windshield. For those looking to increase mpg you may want to use the degog setting sparingly. I'm too lazy to look for the thread on fuel saving tip but if you're following it you may want to add this.

Re: Learned something on nasioc today
 

All cars turn on the compressor on the defrost setting...By using the freon almost all humidity is taken out of the air that comes in which in turn gets rid of the "fog" quicker. Also other cars that may have a setting for air by the feet and defrost at the same time, most will also turn on the compressor for that. However in my 95 cutlass when on the feet/defrost setting it would not turn the compressor on and so I never turned that car on full defrost. Just something to check out.

Edit: I should say every car that I know of. There may be a slight few that may not work this way.

Re: Learned something on nasioc today
 

This is a good point Michael.

Just for the sake of the good running of your aircon system you should run the system in defog or defrost at least once a week in the winter. This ensures your compressor stays in good working order. It is assumed you will use it fairly often in Summer to keep the car cool. ;)

Auto Express in England ran some comparative tests recently in search of economy. They used a diesel car for the tests, I suppose it is possible a petrol car may have given different results [because the diesel engine has more torque available at low revs compared to a petrol engine].

Anyway they found that most of the things we are warned against made very little difference to overall mpg. These were things such as driving with a roof rail, driving with windows open, tires too soft etc. These only made 1 or 2 mpg difference over the test course.

Driving with the aircon on made a major difference around town, but not a great difference on the highway. Aircon made a 5 or 6 mpg difference in town and a 2 mpg difference on the highway.

This is all related to revs and engine output. Say for instance the SVX engine makes 200 hp at 5000 rpm. In broad terms it will be only putting out 1/5th of this at 1000 rpm, approx 40 hp. We all know the SVX tends to run in 4 range even at low speeds in town. Well at these speeds the engine is giving out 40-50 hp.

When the compressor is on it soaks up 5 hp to drive it, whether the engine is doing 1500 rpm or 5000 rpm.

So at town speeds it is using up 10% of the available power. All the time. So the mpg suffers.

At highway speeds the engine is probably making 120 hp, maybe more, so the 5 hp for the aircon pump is less of a hit.

It does actually pay to switch off the aircon if it is not required.

Joe

Re: Learned something on nasioc today
 

However if you put on defrost + feet, as most vehicles have, it turns the AC off. Then you can tweak the settings to clean up the windshield as best you can. Also some newer vehicles allow you to turn off the AC after it's automatically come on, when using defrosters.

Re: Learned something on nasioc today
 

I run my climate control in ECON, full time. I find it does an acceptable job of clearing fog off the windshield. My car never frosts on the inside, so there's nothing I can't scrape off before hitting the road.