Possible Dumb Question Alert (A/C and MPG) - Honda Prelude Forum

Padge · 07-03-2002, 12:02 PM

Sorry if this question is extremely ridiculous, but the past two weeks here in PA have been intensely hot with heat indexes hitting 105. Air conditioning has been a must lately during my rides to and from work, but I hate having to turn it on because I know my fuel economy drops drastically as well as my ludes performance. So here are the dumb questions:

1. The a/c (vents) blow at 4 different levels from low to high, if I have the vents set at high, will this require more gas then having the A/C blowing out at a lower level?

2. Or... does having the A/C set at low have the same effect on fuel economy and performance as having it on high, in other words no matter how high the A/C is turned up, the affect is the same?

If you guys dont get what I am asking sorry. I just dont really understand very well how A/C works. Thanks alot

Shammy · 07-03-2002, 12:05 PM

Okay, here's how I understand it. The speed at which the air blows is a function of an electric motor in the dash (same one that runs the blower for the heater?) So, having the fan on high doesn't use any more gas than the fan on low.

Make sence?

Padge · 07-03-2002, 12:11 PM

so setting it high or low requires the same amount of fuel? So i mine as well blast it if I have it on... right?

supabill · 07-03-2002, 12:11 PM

thats what ive heard too...High low medium who cares...you lose the fuel economy and performance from it just being "on"

marcucci · 07-03-2002, 12:14 PM

Quote:

Originally posted by Padge
Sorry if this question is extremely ridiculous

There are no stupid questions, only stupid people.

Quote:

1. The a/c (vents) blow at 4 different levels from low to high, if I have the vents set at high, will this require more gas then having the A/C blowing out at a lower level?

Yes and No. The blower is electric and consumes power when on (as alternator load increases, load on the engine increases), but it consumes the same amount of power regardless of speed. Resistors are used to drop the speed but the same power is consumed regardless. The speed has an effect on the BTUs or amount of "work" the compressor is doing, though. With the blower on high you move more air and thus provide more heat for the compressor to have to remove. It cycles "on" longer (compressor normally cycles like your one in the house) making it work harder. This would make a drastic difference if you are using fresh air (instead of recirc) and you're talking the difference between 1 and 4.

Quote:

If you guys dont get what I am asking sorry. I just dont really understand very well how A/C works. Thanks alot

Check out

http://www.howstuffworks.com

Might help you out. Basically the A/C just moves heat- it pulls it out of the cabin and moves it to the coils in front of the radiator. The more air (heat) you move, the harder it works. Use recirc, that's the single best thing you can do to improve the system's efficiency (that and cleaning the bugs/dirt out of the coils). You cool the already cool air which reduces the amount of heat the a/c has to remove.

brendon2k · 07-03-2002, 12:35 PM

Quote:

Originally posted by marcucci

Use recirc, that's the single best thing you can do to improve the system's efficiency (that and cleaning the bugs/dirt out of the coils). You cool the already cool air which reduces the amount of heat the a/c has to remove.

This help a ton in my car. When I got in an accident they redid the a/c and upgraded it to the newer stuff r-34(??). I live in the desert and with it not on recirculate the air is slightly cooler but not enough to fight the heat being added from the sunlight coming in. The result was my car couldn't get below 90ish. With recirculate on it can actually start to get cold air to blow out after a few minutes.

Mugenlude · 07-03-2002, 12:38 PM

As always, Todd has answered the question plus some. Thanks as always.

ThatPreludeGuy · 07-03-2002, 12:40 PM

I find my A/C doesn't affect my mileage a noticable amount. Maybe I drive like a normal person when it's on since the power is lacking....

Padge · 07-03-2002, 12:40 PM

Great, I appreciate everyones help. I get it now, I used to be at www.howthingswork.com all the time, I guess I forgot about it. Anyway, thanks again.