A/C constantly activated - good or bad?

[Bamaro]

Originally Posted By: itguy08
Originally Posted By: pezzy669

I never really thought about the MPG penalty, did not figure it was too much. Maybe will try a tank without the a/c and see what happens. My commute generally does not change so it should be a good comparison.


There is little to no MPG penalty with a modern cycling compressor system. It will only run the compressor long enough to satisfy the need to cool the evaporator and then switch off. It won't run all the time like the old systems used to.

With todays cars so aerodynamically tuned, opening the windows/sunroof kills aerodynamics and extracts a larger MPG penalty than the A/C.

I've got auto A/C and just let it do its thing. Never an issue and something IMHO is nothing to worry about. Us shadetree types are not smarter than the guys that design this stuff for a living.

As the saying goes, There is no such thing as a free lunch.

 

[CROWNVIC4LIFE]

Since the early 70's I leave mine on all the time 365 days a year..I just set it and forget it..I manage to put 200-300K miles on all my cars without a/c issues..For cars that did not have the automatic position I used the Bi-Level position..It is generally the people who constantly turn the a/c on and off all the time who have the most issues.

I noticed zero engine load on my 5.0 and 4.6 Panthers and other cars I have owned..One time a few years ago during the cooler weather I did turn the a/c system off for a couple of days just to see if there was a difference in gas mileage..It was maybe 1%..I get around 25 MPG on my runs from Miami-N.Y.C. with the a/c running constantly.

I have no idea why so many people make it such a big deal running the a/c all the time..Even in N.Y.C. I left the system on all the time all year long.

I could never figure out the window crackers..Who really wants hear all that wind and road noise out there on the highway.

Down here in the jungle with tons of road construction everywhere,dust,landscapers everywhere you go and constant passing showers you go really do not want the windows down at anytime.

 

[HerrStig]

Originally Posted By: rshaw125
Originally Posted By: coolbird101
My experience with auto ac is the more it is used the less likely problems will occur, the reason to run at least once in awhile is to keep orings and seals lubricated or they will dry up and leak. Oil travels with the refrigerant.


Do you run your home AC during the winter? I don't. I also pull the relay on my car for the 4 coldest months so the car AC does not run. Never had a problem when I start using it again.
If it's a heat pump you do.

 

[HerrStig]

The energy required to turn an AC system compressor when the condenser is cooled by cold winter air is MUCH less than when you are trying to keep a car interior at 70 degrees when it's 90 outside and the condenser is tasked with dumping heat into it. Those of us with "manual" AC note the difference in drag when "pushing the button" in cold weather. Since I have a switch, I don't us the AC on a cold dry day, but when it's cool and damp, the car interior stays dry without much of a fuel penality with it engaged.

 

[Thermo1223]

Originally Posted By: Smokescreen
"There is little to no MPG penalty with a modern cycling compressor system."

There are entire website forums full of hyper-milers that will disagree with this statement and have scads of data to back it up.


I think where he was going is these days a lot of cars use vari-displacement compressors so they are not running at full load constantly.

I know VW/Audi has used them since the late 90's and I'd assume some other Euro makes might has as well.

There will always be some energy used but hypermillers tend to exaggerate their findings much like their driving styles...

 

[Smokescreen]

" There will always be some energy used but hypermillers tend to exaggerate their findings much like their driving styles..."

...and making this statement clearly displays how little you know on the subject.

 

[Thermo1223]

Originally Posted By: Smokescreen
" There will always be some energy used but hypermillers tend to exaggerate their findings much like their driving styles..."

...and making this statement clearly displays how little you know on the subject.


Really, because what I find to be efficient and SAFE driving differs from a lot of what the hypermillers think. I know enough to know it is not in the best interest of safety and that alone makes it undesirable. No change in fuel economy is worth running tire pressures at limits exceeding sidewall pressure ratings. Saving 1 gallon of gas is not worth doing pulse & glide or lower than traffic speeds on any road.

So sorry my understanding on the subject is quite sufficient. I do not have to do it myself to know what they refer to as driving and I do are wildly different concepts. I will leave it at that.

 

[rjundi]

Originally Posted By: rshaw125
Originally Posted By: coolbird101
My experience with auto ac is the more it is used the less likely problems will occur, the reason to run at least once in awhile is to keep orings and seals lubricated or they will dry up and leak. Oil travels with the refrigerant.


Do you run your home AC during the winter? I don't. I also pull the relay on my car for the 4 coldest months so the car AC does not run. Never had a problem when I start using it again.


You saving it? Winter means moisture potential and foggy windows. AC IMHO is a safety requirement for myself.

 

[antiqueshell]

The best way to prolong life of AC systems in vehicles is to make sure you use the AC at least biweekly or so to keep the oil circulating through out the system. It only needs to be about 10 minutes or so.

 

[rationull]

My Subaru has auto climate control and it behaves the same way -- AC is nearly always on, hot or cold. The one exception is that on cold mornings with the heat turned up, it will not turn on the AC until the heater warms the cabin up a bit.

It annoyed me for a while, just due to lack of control, but I've gotten over it and pretty much let it do its thing.

 

[itguy08]

Originally Posted By: PFP

Have you done a test with it on and then off? I have, in 2 American and 2 German cars, model years 2002-2010. In each car, there was a 10% penalty with a/c on, windows up, compared to a/c off, windows down.

Our local paper ran a test in its automotive section and found the same results, as have others.

In each of my car, there was noticeable power loss with the a/c turned on, as well.


I have not as I seriouslu doubt I'd go from an average of 20 to 22 MPG with turning the AC off. The route I drive can have the same impact. The route you drive and the amount of city vs highway plays a huge difference. As does the driver.

Get stuck with more red lights during one test? Your MPG will go down. Get behind a slowpoke your MPG may go up. Feel a little "frisky" with the go pedal and it will go down. Heck, even subconciously you could affect it in the way you want to affect it by altering your driving style ever so slightly.

The "best test would be to fill up the tank, get on the highway and set the cruise. Drive, say 25-50 miles in a round trip. Fill up again, get back on the highway and repeat. That way you get the human factor out as best as you can.

And as for the hypermiler sites - I'll say what an old boss said when I was complaining I was underpaid to what salary.com said I should be getting. "Those sites are exadurated. Nobody is going to tell the truth to make themselves look bad - people will inflate the #'s to ake them look good." After thinking about it, it makes perfect sense...

 

[itguy08]

Originally Posted By: cjcride

Orville and Wilbur Wright were "shadetree" guys.


We're also not inventing something. Trying to reinvent the wheel so to speak. In the race for higher MPG do you not think automakers are looking at every optimization to get that last mile out of the last drop? Of course they are. It's a lot simpler to optimize existing systems rather than design new.

If it were as simple as disabling the AC to puck up 10% MPG gains they would do it or scale back the time it runs by a HUGE amount. And they are not.

 

[KrisZ]

Originally Posted By: itguy08
If it were as simple as disabling the AC to puck up 10% MPG gains they would do it or scale back the time it runs by a HUGE amount. And they are not.


You have to stop looking at this as black or white scenario. Tell me how many people would buy a car with no AC?
Automakers know that comfort is a huge factor for commuters and that is why AC is used a lot in today’s HVAC programming, not because it does not affect mileage.
And they are scaling back the use of AC. That's why we have variable load compressors and lots of sensors inside the cabin to ensure the comfort of passengers with as little AC load as possible to minimize gas mileage penalty.

That's the same approach as in the home high efficiency HVAC systems. You have 2 stage or variable load systems that use as little electricity as possible to keep people inside the house comfortable, but they still use extra electricity. There is no free lunch.

 

[Win]

Aren't all modern compressors variable displacement?

The two Jags and the G8 have automatic climate control, so the compressor runs all the time (although it can be overridden), no problems so far.

The two remaining Pontiacs have manual control, but I always leave the compressor on. The BCM will automatically turn them off if it is too cold outside.

 

[SteveSRT8]

Originally Posted By: Win
Aren't all modern compressors variable displacement?

The two Jags and the G8 have automatic climate control, so the compressor runs all the time (although it can be overridden), no problems so far.

The two remaining Pontiacs have manual control, but I always leave the compressor on. The BCM will automatically turn them off if it is too cold outside.


Can't think of one that isn't. Our GMC products don't even allow you to mess with it, but it does quit running in the winter if you set the heat high long enough. The Chrysler has a kill button if you just got to.

I don't see the problem. There is very little lost to a modern car's AC compressor, probably at least as much running the gargantuan electrical loads (blower, etc.)!!

 

[lexus114]

Originally Posted By: pezzy669
So I have a question that has been on my mind for ~3 years since I purchased my '10 Mazda 3.

I have the dual zone automatic climate control in my 3 which works brilliantly - works surprisingly better than the auto in my spouses '08 BMW 128i. Anyways both of our cars the Auto On switch pretty much works as an a/c on switch. AKA system on, a/c on. Doesn't care exterior temp, mode, etc. it is going to run the a/c compressor. Granted the compressors will not engage when the exterior temp is below whatever minimum temp threshold programmed into the system - a/c switch light will still illuminate.

So since our cars were new the a/c has always been run - figure there was some logical reason determined by BMW and Mazda to run the compressor so we just let the cars do what they want to do. On top of this my father always taught me that you need to run the a/c at least once a month to keep the oil circulating or else you are asking for problems.

Thoughts? Premature wear or keeps the system in good condition?




This is odd because I can shut off the A/C when in the auto position whether on my car, or my wife`s car.

 

[Bamaro]

Originally Posted By: SteveSRT8
Originally Posted By: Win
Aren't all modern compressors variable displacement?

The two Jags and the G8 have automatic climate control, so the compressor runs all the time (although it can be overridden), no problems so far.

The two remaining Pontiacs have manual control, but I always leave the compressor on. The BCM will automatically turn them off if it is too cold outside.


Can't think of one that isn't. Our GMC products don't even allow you to mess with it, but it does quit running in the winter if you set the heat high long enough. The Chrysler has a kill button if you just got to.

I don't see the problem. There is very little lost to a modern car's AC compressor, probably at least as much running the gargantuan electrical loads (blower, etc.)!!

There is no comparison of power loss between a compressor and fans/alternator. Compressor loss is much more.

 

[SteveSRT8]

Originally Posted By: Bamaro
Originally Posted By: SteveSRT8
Originally Posted By: Win
Aren't all modern compressors variable displacement?

The two Jags and the G8 have automatic climate control, so the compressor runs all the time (although it can be overridden), no problems so far.

The two remaining Pontiacs have manual control, but I always leave the compressor on. The BCM will automatically turn them off if it is too cold outside.


Can't think of one that isn't. Our GMC products don't even allow you to mess with it, but it does quit running in the winter if you set the heat high long enough. The Chrysler has a kill button if you just got to.

I don't see the problem. There is very little lost to a modern car's AC compressor, probably at least as much running the gargantuan electrical loads (blower, etc.)!!

There is no comparison of power loss between a compressor and fans/alternator. Compressor loss is much more.



Uh, you might want to check that comment. Modern variable displacement systems use very little HP.

I have one car that can draw nearly 50 amps on max blower setting!!!! Hardly insignificant, especially here in FL where we run air almost all the time.

 

[Smokescreen]

Here is a good read for all the naysayers, broken down by state for even further interest: http://www.nrel.gov/vehiclesandfuels/ancillary_loads/pdfs/2002_01_1957.pdf

Unfortunately, even with copious amounts of scientific data there will be those that don't choose to compute it, digest it and move on. Willingness to learn is a choice, I understand. The conclusion of the paper pretty much wraps it up quickly for those who don't want to go through the process of chewing every bite.

As far as hyper-miling techniques go, there are some that are wacky enough to push safety to the limit, BUT the vast majority of those that wish to save fuel simply don't do those. Like anything you get extremists that push the boundaries. But for the most part, most of it is simple common sense, many of the ideas and techniques used 20 years ago are being implemented in new cars today. Stop/start technology, accelerator pedal input modulation, pulse and glide, cylinder deactivation, grill shutters, even aero-dynamics general shapes from studies 30-40 years ago are being put into place as drivers begin to recognize the need for them and accept them. In looking at even this simple link: http://ecomodder.com/forum/EM-hypermiling-driving-tips-ecodriving.php ... you'd be hard pressed in finding anything that wasn't common sense with a basic understanding of physics. A good driver with a small inclination of fuel savings could ace any non-believer with one simple technique quite handily. http://www.fueleconomy.gov/feg/drive.shtml or http://oee.nrcan.gc.ca/cars-light-trucks/driving/fuel-efficient-driving-techniques/17823 etc, etc

 

[Smokescreen]

Back on topic.

In some regions the climate is such that when one runs the A/C all the time the differential between the hot ambient air and the cool evaporator causes quite a bit of moisture within the dark recesses of the HVAC piping. This makes a perfect environment for mold spores to form on the interior evaporator. Result is a locker room stink that can be difficult to get rid of usually treated somewhat successfully with Lysol or other air disinfectant sprayed into the air intake. Usually happens more when the setting is Max A/C or recirculate. The natural remedy would be switching off the A/C with the fan still blowing to dry the evaporator off so that mold doesn't form in the first place, but you will still see people running to the dealership saying my A/C is broken yada yada.

Mechanically I have seen to many references to count that running the A/C at least once a month keeps the seals sufficiently lubricated so that they don't leak and it exercises the system, and that makes sense. Having worked with coolers and freezers for some time in a commercial environment, I can say that the condenser units do not run all the time. They have cool down periods, defrost periods all built in. I am not say that they can't, I am saying that they don't from my experience. How that translates to the car environment YMMV.