Does AC effect power or mileage??

[BoostedLegacy]

I have a Legacy Turbo and when I got the car the AC belt wasn't on. My conclusion is that it either ran out of refrigerant, or someone thought they would achieve better horsepower or better mileage by removing the belt. I don't know about it increasing the horsepower, but I suppose I could see it effecting the gas mileage. Gas mileage is great, but its freaking hot. Is the gas mileage worth frying over??

[idosubaru]

if you're driving with the windows down at highway speeds, on many vehicles it's worse on your mileage or a negligible difference anyway than using your a/c.

 

try and turn the a/c compressor by hand. if it doesn't freewheel at all, then the bearings are shot and that's why they removed it. then try to turn the center portion, it should be tight, like turning an engine over as it compresses internally, if that doesn't move at all or feels rough/makes noises then the compressor is shot. if it appears to be working fine then throw a belt on it.

 

it can affect mileage and performance some but it isn't much and would only make a noticeable difference if it's on. if it freewheels fine, which you can check and you don't use it, you won't notice anything at all. i think the XT6 has a mechanism by which if you're inducing a certain amount of load on the engine it temporarily disengages the A/C compressor, pretty sure i read that in the FSM because i certainly wouldn't make that up. if that's the case, i wouldn't be surprised if the legacy does the same thing. if not you could wire that up yourself.

[BoostedLegacy]

if you're driving with the windows down at highway speeds, on many vehicles it's worse on your mileage or a negligible difference anyway than using your a/c.

 

try and turn the a/c compressor by hand. if it doesn't freewheel at all, then the bearings are shot and that's why they removed it. then try to turn the center portion, it should be tight, like turning an engine over as it compresses internally, if that doesn't move at all or feels rough/makes noises then the compressor is shot. if it appears to be working fine then throw a belt on it.

 

it can affect mileage and performance some but it isn't much and would only make a noticeable difference if it's on. if it freewheels fine, which you can check and you don't use it, you won't notice anything at all. i think the XT6 has a mechanism by which if you're inducing a certain amount of load on the engine it temporarily disengages the A/C compressor, pretty sure i read that in the FSM because i certainly wouldn't make that up. if that's the case, i wouldn't be surprised if the legacy does the same thing. if not you could wire that up yourself.

Cool that was a big help. I'm gonna try and get my ac working

[BoostedLegacy]

Bummer, just checked it. Looks like the AC pump is toast.

[Manarius]

I think the A/C disengages at WOT.

[eryque]

A/C does in fact take away both power and gas mileage. How much it does this varies. In my 2.2L Impreza I get 22 mpg w/ the A/C on and about 29 with it off.

[BoostedLegacy]

A/C does in fact take away both power and gas mileage. How much it does this varies. In my 2.2L Impreza I get 22 mpg w/ the A/C on and about 29 with it off.

 

Wow that is a huge difference. It gets bad enough as it is. About 19 in the city and 25 on the highway. As soon as that boost kicks in my gas needle just drops....

[idosubaru]

Depends on your driving style and habits as well. For highway mileage on some vehicles you'll notice little difference, i haven't in my 1997 2.2 liter OBS...... of course the caveat to all of this is if your vehicle is running good. one that is running poorly won't help your numbers either way.

 

as to your compressor being shot. if it's a simple failure you can just get a used compressor for $25-$35, charge it yourself and be good to go. if it puked up pieces all through your system then youll need to replace a lot of parts to get it back and running again without destroying your next compressor you install. if you open anything and see lots of black or pieces in the system, then you might as well forget it unless you want a rather large job and expense. i suppose you could try and source all used parts, but even still i can't imagine it being less than $100-$200.

 

now, if you're really lucky the compressor does have a bearing that can be replaced on the vehicle without discharging the system. i've never done it, but others have. if this bearing is frozen you might be in for an easy fix, without discharging the system or replacing your compressor. use the SEARCH button here and you should find some info on how to replace this bearing and a part number for it as well. subaru will look at you cross eyed if you ask them, they'll say you need a new compressor. ..when really you need a $2.00 bearing. does the pulley free wheel at all? in other words if you try and spin it, does it turn? if not, then this may be the easy to replace bearing.

[nipper]

Blu in summer gets 19 w/ac 21 without ac. On the highway it seems the same either way, or its so close that it doesnt matter.

 

On a tank to tank basis, it may cost you 4-5.00 to run the ac per tank. Personally thats fine with me if it keeps me from cooking.

 

nipper

[Dickensheets]

Blu in summer gets 19 w/ac 21 without ac. On the highway it seems the same either way, or its so close that it doesnt matter.

 

On a tank to tank basis, it may cost you 4-5.00 to run the ac per tank. Personally thats fine with me if it keeps me from cooking.

 

nipper

 

My 97 obw gets about 26 all around. My miles are mostly hwy miles. I run the ac if speeds are above 45mph, below that I run with the glass in the retracted position. I think if you slow down about 5-8mph on the hwy the effect of the ac is not noticeable.

[BoostedLegacy]

Depends on your driving style and habits as well. For highway mileage on some vehicles you'll notice little difference, i haven't in my 1997 2.2 liter OBS...... of course the caveat to all of this is if your vehicle is running good. one that is running poorly won't help your numbers either way.

 

 

Yea it runs great. My problem is driving to fast. it's not that I constantly have it at redline or something, in fact I don't think I've had it at redline, but its so easy for me to mess around in that thing. Especially if its slick out, thats why i keep going through axles....in the long run i waste a lot of gas. If i drive normal it actually gets pretty good gas mileage...

[Olnick]

. . . you might be in for an easy fix, without discharging the system or replacing your compressor. use the SEARCH button here and you should find some info on how to replace this bearing

 

Grossgary, you've mentioned this several times but I've searched and have never found anything about it. Can you offer any links or search suggestions?

[Manarius]

One number I heard was when you have the A/C on, you lose about 30hp. Maybe that was a gross overestimate, but on my NA 2.2 Legacy with 130hp, it certainly felt like a 30hp loss.

[idosubaru]

Grossgary, you've mentioned this several times but I've searched and have never found anything about it. Can you offer any links or search suggestions?

"compressor bearing" brings up many threads that mention it. this one shows an exploded picture of the bearing:

http://www.ultimatesubaru.org/forum/showthread.php?t=58635&highlight=compressor+bearing

 

i'm not going to search through them all, but there are more out there, including some replies from people that have actually done it.

[nipper]

One number I heard was when you have the A/C on, you lose about 30hp. Maybe that was a gross overestimate, but on my NA 2.2 Legacy with 130hp, it certainly felt like a 30hp loss.

 

Its about 5hp. In all the years that AC has been on cars, its never been 30hp. Alo somone who is better in math then me can prove it mathmatically that it is about 5hp.

 

nipper

[Virrdog]

Its about 5hp. In all the years that AC has been on cars, its never been 30hp. Alo somone who is better in math then me can prove it mathmatically that it is about 5hp.

 

nipper

The rubber belt could not even hold the shock load of pulling the engine down 30hp over and over again... It would break or slip.

[Manarius]

Meh. It may only be 5, but it felt like 30

[uniberp]

if you're driving with the windows down at highway speeds, on many vehicles it's worse on your mileage or a negligible difference anyway than using your a/c.

 

I t'ink dis was completely busted on "mythbusters".

 

I s'pose "some vehicles" could include airplanes, do'.

 

My experience on all vehicles is AC~= 18% loss, windows don't matter.

[nipper]

I t'ink dis was completely busted on "mythbusters".

 

I s'pose "some vehicles" could include airplanes, do'.

 

My experience on all vehicles is AC~= 18% loss, windows don't matter.

 

Mythbusters is as accurate as the Enquirer or Weekly World News. Its an entertainment program, not based in facts.

 

The magical number is 40mph. Below 40 mph is considered city driving, and the car gets the best mileage with the ac off and the windows open. Below 40 there is enough "urban" noise that some wind noise is acceptable. Above 40mph is considered highway driving, and where the car is aerodynamically designed. The testing is done with all the windows up to minimize drag. Opening the windows creates alot of drag. At highway speeds wind noise is an undesireable effect.

 

 

nipper

[NV Zeno]

When the temperature is above what my comfort level happens to be that day, the minimal dollar costs or power loss (if there actually are any) by running the A/C simply do not outweigh being comfortable. Ever.

 

My 2 bucks

[BoostedLegacy]

When the temperature is above what my comfort level happens to be that day, the minimal dollar costs or power loss (if there actually are any) by running the A/C simply do not outweigh being comfortable. Ever.

 

My 2 bucks

 

I agree actually. I wouldn't use it all the time, but on those really hot days, I'd end up spending a few dollars in drinks anyway....

[Olnick]

"compressor bearing" brings up many threads that mention it. this one shows an exploded picture of the bearing:

http://www.ultimatesubaru.org/forum/showthread.php?t=58635&highlight=compressor+bearing

 

Thanks grossgary, exactly what I was trying to find. I admit, there are times when I can't get no satisfaction from that search function.

[uniberp]

The testing is done with all the windows up to minimize drag.

 

nipper

What testing are you referring to? Is there a benchmark by a 'reputable' lab somewhere? The mythbusters test, yes I know they are not engineers, was done in identical suvs at a fixed speed, I think 50mph, with windows open ac off and windows closed ac on full.

 

It wasn't a terrible illustration.

 

http://kwc.org/mythbusters/2004/11/mythbusters_boom_lift_catapult.html

 

"Windows down vs. air conditioning

"Urban puzzle": it is more efficient, on a hot day, to run with the A/C on and windows up than to run with windows down (b/c of increasing car's drag).

Computer-based mpg measurements:

• 11.7/11.8 with A/C on and windows up
  
• 11.7/11.8 with A/C off and windows up
  
• 11.3 with A/C off and windows down

So, according to the computer, it's better to use A/C with windows up.

This was too quick and easy for TV, so they decided to stage a seven hour marathon, race-til-you're-empty duel, with Jamie driving an SUV with A/C on and Adam driving an SUV with windows down. Though, once the safety inspector intervened, it was no longer a seven-hour marathon, it was a bit slower (45mph instead of 55mph), and a lot shorter (only 5 gallons each).

Jamie's A/C car ran out of gas first -- Adam's windows down SUV ran for another 30 laps -- completely contradicting the computer mpg estimate. Computer estimate based on air flow into the engine, so it would appear that it is unable to properly model the difference between A/C and windows down."

[idosubaru]

i wouldn't be surprised if cars had different results than SUV's. and it wouldn't surprise me at all if they actually tested a few vehicles (car, truck, SUV) and found the ONE that "contradicted" what people would think or had some quirk to it that made for good television..and that's the one they showed/produced. that's how television works. it's nice what they're doing, but i wouldn't trust it all that much either.

[nipper]

What testing are you referring to? Is there a benchmark by a 'reputable' lab somewhere?

"

 

Its called windtunnel testing. Every single automaker does it, there is no one lab. It is critical to get the drag coeffecient down while keeping the wind noise to a minimum. Thats why subarus don't have rain rails anymore.

 

Every car is subjected to wind tunnel testing.

 

nipper