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Old 07-06-2008, 04:49 PM   #1
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Question -- High Fan or A/C ... Better FE?? --

I know it has been discussed before, I think, but I cant find it!

Whats better, having A/C on low or No A/C but high fan blower?

I ask because the electrical load of high blower might be even worse than low A/C ... ??
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Old 07-06-2008, 05:08 PM   #2
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The traditional way of regulating the blower speed was to have a resistor block, so all the while it's on low, there's a resistor glowing a dull orange under the hood somewhere radiating all that "saved" power as heat.
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Old 07-06-2008, 07:16 PM   #3
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Is it still done that way?

That would be pointless then, if thats the case then I suppose high blower since low A/C is the same PLUS the a/c drag...

??
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Old 07-06-2008, 07:21 PM   #4
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Quote:
Originally Posted by RoadWarrior View Post
The traditional way of regulating the blower speed was to have a resistor block, so all the while it's on low, there's a resistor glowing a dull orange under the hood somewhere radiating all that "saved" power as heat.
Not all of it, but it is significant.
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Old 07-07-2008, 03:02 PM   #5
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I would almost guarantee you that the A/C would put more load on the engine then the fan ever would, even when it is on high. Also, the power consumption with the fan on low, even though there is power dissipated in resistors, is lower than when it is on high.
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Old 07-07-2008, 06:18 PM   #6
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On my '97 Escort the scan gauge shows much higher mpg readings with the fan on high than with the a/c on low. It also shows a/c doesn't effect mileage as bad when you're climbing hills as it does when you're coasting or accelerating down hill.
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Old 07-07-2008, 06:33 PM   #7
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I would almost guarantee you that the A/C would put more load on the engine then the fan ever would, even when it is on high. Also, the power consumption with the fan on low, even though there is power dissipated in resistors, is lower than when it is on high.
I agree with the lower load. A resistor has a set value, while the fan on high has a set vacuum load. Once you start moving air, the amp draw increases, higher than the resistor load would cause.
But, even that said, I can feel the AC clutch kick on, even at highway speeds. With the fan on setting 3 vs. no fan, there is no difference. Only settings 4/5 can I hear/feel a difference in the engine drag. Best use for me is to limit AC usage to flat straights with no cross/head winds and downhills. In town is killer on the accelerations. I always turn the AC off on uphills, even if the car is already getting warm inside. I got 34mpg with that method with 5 people in the car.
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Old 07-07-2008, 07:06 PM   #8
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Quote:
Originally Posted by Ford Man View Post
On my '97 Escort the scan gauge shows much higher mpg readings with the fan on high than with the a/c on low. It also shows a/c doesn't effect mileage as bad when you're climbing hills as it does when you're coasting or accelerating down hill.
yea cause coasting/downhill you're using 2 hp to move and 5 hp for the AC. when you're using 30 or 40 hp to go uphill, the 5 hp for the AC isn't noticed as much in the fuel usage.
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Old 07-07-2008, 08:16 PM   #9
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When the A/C is not in use the compressor is off hence it free-wheels and there is less load on the engine. Once that compressor clicks on it consumes an amount of power that even the highest alternator load wouldn't even come close to matching.

The compressor is activated via an electro-magnetic clutch, when one turns the A/C on if one listens closely one should be able to hear an audible 'click' from under the hood: That click noise is the clutch grabbing between the spinning pulley and the now-loaded compressor, and if you still can't hear the click try opening the hood and your driver's side window now turn the A/C off and on and see if you don't hear it.

The reason you can hear that noise is because the demand from the compressor is such that it takes more torque than puny little temperature activated clutches or what have you can generate, that electro-magnetic clutch is no joke, that piece in and of itself is a $100 dollar part and is roughly equivalent to the clutch that is in use between the engine and the blades of a lawn mower.
That is how much power that compressor needs.

As for the fan drawing power, it gets its power from the battery not the alternator. The alternator merely recharges the battery as it loses power but the alternator in and of itself does not power the fan, the battery does... Meanwhile the car is constantly consuming electric power, there is a constant drain on the battery whether you use the fan or not and the alternator is always putting out power anyhow, and the use of that fan makes little to no difference.
To say the least there is no 'click' from an electro-magnetic clutch having to activate underneath the hood in order to satisfy some sudden demand lol.

So to answer the question...
It would be more economical to turn ALL electrical items on (including headlights and wipers and hazard flashers and fan and radio) while keeping the a/c off than the other way around.
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