After reading the part in my owners manual about the A/C compressor coming on when you turn the dial to defrost, I wanted to do a little checking to see if that was true. If it was, then everytime you defrost your front windshield, you are taking away power from the engine (108hp) to run the A/C compressor.

Here's what I found : It's true, no matter what temperature you have selected (hot or cold), whenever you turn the dial to the right towards defrost, the compressor runs.



As the picture show, this is the last position on the dial that the compessor DOES NOT run. Any more clicks to the right turns on the A/C compressor, regardless of temp. setting, and robs us of valuable hp's.

At this setting on the dial, you still get a little air out of the defroster vents, but not as much as if you turned it more to the right. So I just leave it set right there unless I really need to defrost, like a rainy or snowy night. But after bit starts to clear the windshield, I turn it back to this setting for max power.

 

Haven't all cars made in the last 20 years ran that way?

 

I don't understand the point of running the AC compressor when you're trying to defrost. Doesn't the AC compressor make COLD air? I'm cornfused. :?

KiL

 

It dehumidifies the air. Easier to defrost with dry air than with wet air.

My '96 ford was the same way, and my parents had an '82 oldsmobile that was that way too.

 

Tis true. My last car, an '89 Ford Mustang did this, only on it I could tell when the A/C came on, severe power drop. On the xB It's a lot more difficult.

 

Hmm.......didn't know this.

Thanks for the info.

KiL

 

Yes this is true about the a/c comming on when you select defrost. However, the compressor is working less than if you hit the a/c button. This feature, Im glad toyota incorperated! With my old Focus, the a/c would come on full blast (drop in RPMS, engine bog ect..) when you selected defrost- versus the Scion, Were the a/c Is hardly felt with the normal a/c- and almost non existant when the defroster is on...

 

maybe this is one reason why my gas mileage has been so bad since it got cold

 

[quote="mfbenson"]It dehumidifies the air. Easier to defrost with dry air than with wet air.quote]
yes!
and always clean your inside glass so you would not see streaks!
And do not use your bare hands to wipe the glass!

 

OK, so I don't have an xB yet but my Prelude does the same thing, but the light on the A/C button comes on and If I hit the A/C to turn it off, it turns off that compressor from what I understand. So, when you turn it to defrost, does a light come on for the A/C button?

 

the light does not come on.

 

On most cars, not only does the AC compressor come on, but the system switches to 100% outside air as well.

When you have a person (or people) breathing inside the vehicle, it adds moisture to the air. Since cold air can hold less moisture than warm air, even the small amount exhaled during breathing can significantly increase the relative humidity in the car in the winter months. If you are trying to defrost the windshield it is difficult to do with the moist air from inside the car. In winter, the outside air is dryer and then running it through the AC condenses more moisture out of the air stream so the air is as dry as they can get it. Just as a side note, it is also helpful to open your front windows a small crack to allow the air to draw across your windshield and out of the car when in 100% defrost mode. Since all the air is coming from outside, it has to be relieved back out of the cabin.

I'm not sure if the Scion defrost system automatically switches to 100% outside air but it is a good idea to switch it over to get maximum defrost capacity from the car. Once the inside of the car warms up, the air can hold more moisture so you could switch back to recirc on the air stream if you want to get more heat into the cabin.

 

modern cars don't use too much power with AC. I know our engine is small, but I just saw on myth busters that a SUV they tested on there got the same distance with a tank of gas with or without the AC on, but if they rolled down the windows the extra drag would lower their MPG. So it's cheaper to run with AC on than windows down now.. but more importanly the drop in MPG with the AC on was almost not measureable. (that was with a bigger engine though). I can't feel the AC come on in my xB.

 

Yea, you really don't feel the power drop with the xB, or you don't feel the compressor kick on either. That's because it such a small little compressor. That's why it has a hard time cooling on a hot day. It's a real tiny as compressors go, but so is the engine, and the power drop ans fuel economy drop IS there.

But the reason for my post was that I wanted everyone to know it comes on in a position on the dial long before you would expect it to. And the odd thing is, on any car with a A/C switch, you usally had to push it on to get the compressor with defrost, or the light came on when you went to defrost. With the xB, it seems to be automatic, but with a switch also. Hell, they could have just added a couple more positions on the dial and just left the A/C switch out all together, like most American cars.

 

no, it started with the imports...
and some current cars don't do that yet...

 

another thing, if your worried about losing power...if you floor it, the A/C turns off...

 

really? cool.
Another funny thing is the recirc/fresh air.. seems and feels like you can mix the two, as though it's a slide with a cable.. but it's a switch, so it's one or the other. I laughed when I saw that.

 

yeah, i laughed at myself...

i thought i was mixing the air till i took it apart and saw i was wrong....

 

That's good to know also...........Thanks

 

this is old news. At WOT most cars will turn the AC compressor off....