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My sister's A/C is a medical necessity; I charged it yesterday with an Auto Zone recharge product and it is ice cold now in her 1996 Subaru 2.2.  I mistakenly told her that A/C puts a burden on an engine, so she did not use it and developed heat exhaustion after a three plus hour trip and spent two days in the hospital recently.

 

How many people here never or almost never use the A/C in their cars?  How much does its use affect miles per gallon and other issues?  Thank you!

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measure it yourself.  tell her to run the a/c every day when it's hot.  then where there's a cool snap, quit using it and compare gas mileage.  or keep track for one month now and one month in the fall before fuel mixes change.  cool weather should come soon enough for you NE'ers.

 

run the A/C, it's a negligible difference in gas mileage.  i'm active and healthy but get severe headaches and migraines if i loose too much water, and i'm generally hot natured, so while i can tolerate heat just fine i know better and will pay for it the next day.  so i often run the a/c when i don't necessarily want or feel like i need to.

 

the effect on gas mileage is dependent on quite a few things.  the lighter you are on the gas pedal and the less labor heavy your driving needs are (heavy loads, towing, driving in mountains, sitting at idle, accelerating a lot, cruise control useage, etc), the less the a/c effects mileage.  there's a lot of variables, but yeah i'd expect a small load on the engine in general.  and then there is vehicle condition too.....which varies considerably on a 15+ year old car, even two that are running great.

 

charging your phone puts a small load on the engine, putting weight in your trunk puts a small load in your engine. 

 

keep track of mileage and find out for your given vehicle

 

in other words i've had a/c basically have no effect at all when driving all highway miles at 60 mph for an entire trip.  i've also had it knock down mileage when it causes the car to downshift frequently on every mountain grade....

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if it's loosing refrigerant, which it probably is if you had to charge it, then be sure to replace the two orings on the compressor next time it's low.  those two orings fail all the time and the others basically never do.  so you got a really, really good shot at fixing the leak by replacing two really cheap orings that take like 20 minutes or less.  very easy.  i guess it's due to engine heat and vibrations due to the a/c compressor itself and being right on top the motor. as soon as you remove them you'll see how hard and brittle they are.  all the others are usually still soft and maleable.  i replace these things all the time.

 

here's a write up about it on my 2002....the 1996 won't be much different, i just did the exact same compressor, was really easy.

 

http://www.ultimatesubaru.org/forum/topic/127980-diy-ac-air-conditioning-leak-refrigerant-repair-for-5-or-less15-m/

Edited by grossgary

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I seem to recall reading somewhere that most cars with the AC on and windows up get better mileage than the same car with the AC off and windows down. Something to do with drag. 

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I seem to recall reading somewhere that most cars with the AC on and windows up get better mileage than the same car with the AC off and windows down. Something to do with drag. 

 

Yup, this is true. I believe that <45 MPH, you'll get better gas mileage with the windows down and A/C off. But at >45 MPH, you'll get better gas mileage with windows up and A/C on. Once you get up to freeway speeds, the drag is immense. You can notice a difference in how much harder it is to accelerate at 70 MPH than it is 60 MPH (with the windows down).

 

Now, the guys on the show, "Mythbusters" did an experiment with this. This was their original episode:

 

 

Like what the top comment on the video says, they're doing this on a powerful Ford motor. A/C won't have as big of an effect on those larger, more powerful engines. However, on our less powerful Subaru motors, the A/C has a bigger effect. The fans of the show wrote in complaining they didn't test different speeds and whatnot. So the Mythbusters went back and did the test again in a sedan, with different speeds (you can search for that video on your own time). They concluded what I said above: there's a certain speed where A/C is less gas consuming. At slower speeds, it's better to have the windows down. At higher speeds, it's better to have the A/C on.

 

I know the A/C in my sister's V8 Mustang is really fuel consuming, which isn't good considering the V8 itself gets poor gas mileage. Now, that's a completely different car/engine than a Subaru, and different cars yield different results.

 

With my EA82 (yes, I know, this is the new gen forum), I've removed the major A/C components in order to save weight, which gives me more gas mileage. But in the end, I think it's negligible. When I bought the car, the A/C was never hooked up, so I couldn't get a before/after reading. But depending on how I drive, I can get 20-30 MPG. I feel if I had (and used) A/C, I would get 15-25 MPG, primarily because I don't go on the freeway often.

 

In the end, I think it depends on the driving you do. Lots of freeway driving would justify A/C. City driving justifies windows down. If you have A/C and it's working well, use it.

Edited by jj421

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Given a choice of running AC or spending 2 days in the hospital, guess which I would choose.

 

Comfort and health issues would be a priority for me.

 

As far as a burden on the engine, I wouldn't even consider it a factor.

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Leaving the AC off in genuinely hot weather is something I'd consider if I were hypermiling or started hearing awful noises from the AC compressor... those are about the only reasons I can think of.

That said... I _do_ occasionally turn it off for a minute when I'm booting the car up to highway speed to merge in. I want that extra 2hp :D

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As I got older, driving my A/C-less 1981 Civic wagon began taking a toll on me in extreme heat. I'd have a headache and sometimes feel nauseated by the time I got home on +100 days.

 

Run the A/C.

 

make sure the system is working well, get a hose and blow dead bees and debris out from the condenser and between it and the radiator. Maybe pull some trim/glove box parts off and vacuum out the intake side of the expansion coil.

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For what little that the AC draws on the motor and what you give up in mileage is worth the AC.  I wouldn't be with out it and if it cost me a couple of mpg then so be it. 

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I won't buy a DD car unless is has A/C (and cruise control)....I have to have it. I only run my windows down in the cool of the morning/evening or in the spring time..but anything above 80F and its on.

 

Now to get the most efficient usage out of your A/C place your vent switch on recirculate and never have the fan on full blast, alway at least on setting below full, and as the car cools down more you can decrease the fan speed as well. Also with a lot of the newer cars you can set the temp control to be at a specific setting, this really helps as well. 

 

I won't get into all the technical details of why this works, and how...just take my word for it....unless someone really wants to know, then I can explain...just don't feel like doing that much writing right now. 

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Now that I recharged my A/C and have had it on, miles per gallon definitely dropped; what caused me to not use the air conditioning years ago was the evident poor mileage when it was on, technology has improved however.  My take away on this discussion is to use your discretion, but those who are physically handicapped should use it whenever the humidity and or heat dictate.  Having your sister develop a body heat of 103.5 are require an ambulance and hospital stay for two days after a trip to the beach, is not something that I would wish on others.  

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Now that I recharged my A/C and have had it on, miles per gallon definitely dropped; what caused me to not use the air conditioning years ago was the evident poor mileage when it was on, technology has improved however.  My take away on this discussion is to use your discretion, but those who are physically handicapped should use it whenever the humidity and or heat dictate.  Having your sister develop a body heat of 103.5 are require an ambulance and hospital stay for two days after a trip to the beach, is not something that I would wish on others.  

 

if you are healthy enough that you can tolerate the heat/humidity, then I see no problem "not" using it, but from the sounds of things, your sister should be using it when the heat/humidity dictate she should - regardless of any (relatively minor) burden put on the engine and/or reduction in fuel mileage.

 

I wish the AC in my legacy worked - heat/humidity are not my friend at all - but I cant afford to get it fixed - it is still an R12 system so there would have to be some necessary changes made before it could be operational again.

 

This is also why I wanted "good" parts for the 98 Forester we recently got that already has the R134 system - once it is running again, it can be recharged much easier (& cheaper) than trying to update my current R12 system...

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I wish the AC in my legacy worked - heat/humidity are not my friend at all - but I cant afford to get it fixed - it is still an R12 system so there would have to be some necessary changes made before it could be operational again.


 

 

 

I have converted a number of cars to operate from R-12 to R-134. Simply vac out what is left of R-12, then add R-134. All the talk years back about changing A/C components wasn't exactly true. Sure those changes would make R-134 work better, but I have gotten good results, just swapping in R-134, without doing any of the changes.

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With conversion to R134a there needs to be less volume, by weight, of R134a than the system was designed to use with R12. There are many charts online that will give the weight conversion. Also the fittings for charging must be changed and the receiver/drier should be swapped out (cheap) as well as the o-rings on it's fittings and the compressor fitting o-rings. About 4 ounces of system oil (with UV dye for finding leaks) anytime the drier is changed should be added. Then the system can be safely charged to R134a (to the proper weight).

 

GD

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In my personal experience, the AC does have a very noticeable effect on performance, but NOT mileage.  I seem to get mid 20's regardless of how i drive, but I do a good 50/50 city/hwy.  I suppose If it was straight city only there would be a noticeable difference in MPG.  

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I wish the AC in my legacy worked - heat/humidity are not my friend at all - but I cant afford to get it fixed - it is still an R12 system so there would have to be some necessary changes made before it could be operational again.

 

 

 

I have converted a number of cars to operate from R-12 to R-134. Simply vac out what is left of R-12, then add R-134. All the talk years back about changing A/C components wasn't exactly true. Sure those changes would make R-134 work better, but I have gotten good results, just swapping in R-134, without doing any of the changes.

 

 

With conversion to R134a there needs to be less volume, by weight, of R134a than the system was designed to use with R12. There are many charts online that will give the weight conversion. Also the fittings for charging must be changed and the receiver/drier should be swapped out (cheap) as well as the o-rings on it's fittings and the compressor fitting o-rings. About 4 ounces of system oil (with UV dye for finding leaks) anytime the drier is changed should be added. Then the system can be safely charged to R134a (to the proper weight).

 

GD

 

1. cant afford the parts GD mentions (fittings & dryer) - regardless of how "cheap" they are...

2. Have no way of "vaccing" out the system - I would have to pay someone to do that - again - cant afford it.

3. The Lego really isnt worth putting much (if any) "extra" money into - she is rusting pretty badly...

 

Right now any money being spent is going towards getting the Foz up and running (hopefully with fully functioning AC)

 

So I live with it...It wont kill me, I wont end up in the hospital like the OP's sister (dont have any medical conditions that could cause problems) it is just rather (very) uncomfortable for the duration of a drive - not that I go that far - 30 minutes each way to town & back...if we have to make a longer trip in hot/humid weather, we usually take the other half's 04 Sable, which does have functioning AC...

 

If the heat & humidity are really bad, I avoid going anywhere unless I absolutely have to.

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the AC does in fact put a load on the engine.

it is a very noticeable load in certain situations.

like driving up hill towards home in my 97GT w/ ej22 swap.

of course some of that may be that the car does not down shift soon enough.

 

in city driving i suspect you will see a good bit of difference in MPG.

 

on the hiway i doubt you will notice much difference.

rumor has it that the decreased aerodynamics of the open windows equals the fuel saved by the AC off.

but i don't know.

 

mythbusters did this, google them/ that.

Edited by johnceggleston

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 I'd have a headache and sometimes feel nauseated by the

time I got home on +100 days.

 

as you probably know, but may not, these are symptoms of dehydration, severe dehydration.

the next step is heat stroke.

 

driving in extreme heat, or working or walking or playing or sailing or ......., with a good stiff breeze (5 -10 mph) to evaporate your sweat, will hide / cloud the fact that you are sweating your butt off.

it will not take long to dehydrate if you do not plan ahead or re-hydrate.

Edited by johnceggleston
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