I've been wondering for a while but never have remembered to ask until now. As far as a/c compressors go, is it either on or off? or does your fan setting affect how much of a draw on the engine the compressor is? I was always under the impression that if the compressor was on, it's on and that's it and it doesn't matter how high the fan is on, but the other day a friend of mine said his car accelerates more slowly when the fan's on high than low, which made me wonder. Anybody know?

 

Yes and no.

It is always on, but it's output depends on motor speed. It does eat up some horsepower, especially on acceleration, which is why a lot of people do away with it. It is a pressurized system so it takes power to pump, that power has to come from somewhere - i.e. less is available to the rest of the car when under a load.

That's why a/c works better at highway speeds. It take less power to keep a car going 70mph than it does to accelerate to 70, so that power is distributed to the other systems on the belt driveline. During acceleration, some of the power that is usually available to the wheels is being used to run the a/c compressor. So yes, the more load on the compressor, the more power it will take.

Make sense?




Modified by Lewdin' Incognito at 12:47 PM 8/17/2005

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Lewdin’ Incognito &raquo;</TD></TR><TR><TD CLASS="quote">Yes and no.

It is always on, but it's output depends on motor speed. It does eat up some horsepower, especially on acceleration, which is why a lot of people do away with it. It is a pressurized system so it takes power to pump, that power has to come from somewhere - i.e. less is available to the rest of the car when under a load.

That's why a/c works better at highway speeds. It take less power to keep a car going 70mph than it does to accelerate to 70, so that power is distributed to the other systems on the belt driveline. During acceleration, some of the power that is usually available to the wheels is being used to run the a/c compressor. So yes, the more load on the compressor, the more power it will take.

Make sense?

Modified by Lewdin' Incognito at 12:47 PM 8/17/2005</TD></TR></TABLE>

I understand what you're saying. What I'm curious about is whether the car will make the compressor put a higher load on the system (i.e. increase resistance) if the fan is on a High setting than on a Low setting. For instance, 2 identical cars both have their A/C system on. One has the fan on high, the other on low. All else being equal (negate the small load on the alternator to run the fan at a higher speed) will the car with its fan on low accelerate faster than the other car? Or will they accelerate at the same speed, because the compressor is simply on and the fan has no bearing on the load.

Another question in the same vein: What about temperature settings? For instance, same situation as above, except the fans run the same speed and one car has its temp set at full cold while the other is at about 3/4. Will one accelerate more quickly? Or will they be equal?

TIA

 

I have no doubt that there is increased power consumption between lo/hi fan/temp settings, but the range of difference I wouldn't think would be that much, relative to overall power.

In other words, you'll see the most difference between off and on than you will between on low and on high.

 

There is definitely something that turns on and off. They'll be a little click from under the dash and then I notice the acceleration getting worse and then it will click again and the power comes back.

 

lol i know it goes on and off. I'm just wondering if the system modulates the compressor's resistance (like a sliding scale) or if it's like a light switch, either it's on or it's off. thx for the reply incognito

 

The car will only accelerate slower if the compressor is engaged now when you hear that click thats the compressor is disengaging.
So then you will feel the power come back... the compressor does this to keep the evaporator from icing over so your a/c will actually cool the air thats coming in or thats being recirculated..... But different fan speeds will have no effect on the car acellerating slower with the A/C already on the only difference is how much air is being moved across the evaporator so there might be a bit more load from the expansion valve opening up in the system to help cool the air, but nothing major enough to make it go slower than another car with a lower fan speed.