I'm not particularly familiar with how the air conditioning in my car works, or how it interacts with/affects the engine.

Particularly, i'm interested in how it's powered. I've heard that if you run the air conditioning, it uses more gas. Is this at all true? Where does the A/C system draw it's power from, and if you run it, are there any negative affects on the engine or engine performance?

The A/C is powered by a belt that is connected to a pulley off of the crankshaft. There is a power loss associated with running the A/C.

Get in your car and punch it, about half way through the boost turn on the A/C. You will notice the difference.

Brandon

In the summer in AZ, running AC every time I step into the car, I get about 265-270 miles a tank of gas.

With the AC on just one or two days this month, I am getting 300+ miles per tank.

Not a big difference, but noticeable. Especially back when premium was $2.50 a gallon! (it is down to a sane 1.60 now).

Thanks guys.

hey there is another thing, i noticed with the temp of the air, with the ac running, floor it, the fan still runs, but the air gets warmer, i was told that the car autonatically compensates by cutting out the compressor in the ac unit when you get hweavey on the gas.

I'm curious.. Does the A/C Compressor possibly work less or cycle on and off more slowly when you adjust the temperature control to a warmer setting?

Some nights, I tend to get overpowered by the a/c even on the lowest fan setting; If I turn the temperature control warmer, does the a/c compressor compensate for the change and save me some gas, or does the a/c system just take outside air and mix it with the air from the condenser or whatever, and still eat the same amount of gas and work as hard as if it was on full cold?

I dont recall anything in the manual about this.. ?

i don't think it affects the compressor since it is a closed loop system. the cool air is coming from the blower sucking air from somewhere else and blowing it across the evaporator in the cabin. when you use heat electical coils heat up the air from the blower.

when you use a warmer setting, the refrigerant in the evaporator vaporizes more slowly, and so it requires less work in the same amount of time to compress it into a liquid again. it's a pretty minor effect, though -- probably not noticeable at all...

as for the heat, i'm not sure about newer imprezas, but i know my 96 uses a heater core and not an electric heater -- coolant gets sent from the engine to a miniature radiator that sits next to the blower and heats the air coming in. the result is that you wait longer in the winter for the car to get warm :) if you get in the car when it's cold, you'll notice that the heat only starts working when the temp gauge starts climbing to normal operating range. also a low-temp thermostat would make the wait longer.

on the cutting out the compressor on the gas -- the compressor clutch will disengage when engine temperature gets too high... i hadn't heard of this before, but it very well could be that newer imprezas than mine do have a feature that does the same when the accelerator is depressed past a certain point.

finally, the fan setting doesn't have any effect on the a/c system other than what i said first, where the amount of work the compressor has to do changes because more warm air is going over the evaporator and vaporizing more refrigerant when the fan is on a higher setting.

hope all the useless info helps :P especially since i just noticed the last post was like 3 weeks ago... oh well -- enjoy

You know what sucks... When you turn on the defroster the Air Conditoner Runs no matter what the AC Button Position. Look in the manual it says this! My honda does the same thing but it gives you the option to turn the ac off if you want. On the wrx hiting the ac button when the defrost is on does nothing. Any one know of a way to by pass that auto switch?

Originally posted by meilers
Not a big difference, but noticeable. Especially back when premium was $2.50 a gallon! (it is down to a sane 1.60 now).


speak for yourself, its still 2.13-2.20 here...

Originally posted by JET
You know what sucks... When you turn on the defroster the Air Conditoner Runs no matter what the AC Button Position. Look in the manual it says this!

There is a reason for this- if there is significant water vapor in the air- the water vapor condenses (fogs) on anything that is colder than the air.

Typically when you need defrosting, the windsheild is cold, so if you were to blow moisture laden air on to the cold window- guess what- it will fog up even more!

So by charging the AC system and passing the air over the AC evaporator (the "cold" piece inside the system) your defroster is pulling moisture out of the air before blasting it onto your windows, so it can dry off the window rather than fogging it up.

You might be able to put a switch on the AC, but then your "defroster" setting would only fog/frost things up more.

Don't want the AC system activated? don't use the defrost setting, but really -using defrost without AC is not going to help at all.

Run Defrost with or without air-conditioning mod. Not the type of mod for everyone, but...

http://forums.nasioc.com/forums/showthread.php?threadid=148118

--
0==WW==0
"…axles of evil…" - george w. bush

Originally posted by chubby_one
I'm curious.. Does the A/C Compressor possibly work less or cycle on and off more slowly when you adjust the temperature control to a warmer setting?

Check your owners manual. It turns off the compressor when the engine is under heavy load to make sure that the engine gets the full amount of power needed and for gas economy.