A/C constantly activated - good or bad?

[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?

 

[sleddriver]

The current sled is a '98, so I still have manual control over the A/C. I never set it for 'auto' or a constant temp. I do run the A/C about every 6 weeks if I think of it. Why pay a mpg penalty if you don't need to?

Of course, when it's hot & humid, it's on all the time.

 

[Rand]

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?


I would say its fine.. most systems dont wear out.. their fail isfrom lack of use or seals degrading.(or damage ie crash)

However in ohio I'd have for the MPG penalty of about 10% from the a/c being on.

In a hot state... its pretty much on every day for most of the year anyway.

 

[JHZR2]

I more or less always run my AC. Even in the winter, the dehumidification aspect is valuable. Ditto for cooler but damp weather.

Some owners manuals recommend operating AC at least once a month to keep the seals wet and in good shape.

Ive never found a long duration when Ive ever wanted to keep the AC off.

 

[SHOZ]

I use to pull the fuse for the ac clutch coil in the winter time. Doesn't really make much difference with the gas mileage on my 08 Accent.

 

[KrisZ]

I don't have auto climate in my mazda 3 or the focus, but both run AC when in defrost setting and I always make to use that setting in winter just to run AC. If I had auto climate setting I would just let it do its thing.

 

[Rand]

Originally Posted By: KrisZ
I don't have auto climate in my mazda 3 or the focus, but both run AC when in defrost setting and I always make to use that setting in winter just to run AC. If I had auto climate setting I would just let it do its thing.


This isnt always true.

they run the a/c in defrost if the temp is over 32F-40F usually.

so if its 25F out the defroster shouldnt run(but sometimes will due to heat soak etc)

 

[KrisZ]

Originally Posted By: Rand
Originally Posted By: KrisZ
I don't have auto climate in my mazda 3 or the focus, but both run AC when in defrost setting and I always make to use that setting in winter just to run AC. If I had auto climate setting I would just let it do its thing.


This isnt always true.

they run the a/c in defrost if the temp is over 32F-40F usually.

so if its 25F out the defroster shouldnt run(but sometimes will due to heat soak etc)


My point was that I did it to ensure AC is operated throuought the winter. How the system decides to activate AC at specific temperatures cannot be controlled by me and I don't worry about it. We have plenty of days when it's around freezing temp and the AC definitely runs once everything is warmed up. I even had the compressor activate when it was about -10c outside when I was stuck in traffic.

 

[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.

 

[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.

 

[KrisZ]

Originally Posted By: rshaw125

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.


The reason home AC systems are fine with long periods of inactivity is that all connections are brazed. There are no o-rings, seals or other flexible connections that are exposed to heat, cold, vibrations or need to be lubricated in order to stay flexible. You simply cannot compare the two.

 

[coolbird101]

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.

Yes, I run my home ac in the winter - experiences vary

 

[pezzy669]

I have actually had home HVAC techs tell me (don't know how much weight it holds) that heatpump units typically last longer than standalone a/c because the compressor is used year round. Who knows?

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.

 

[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.

 

[PFP]

Originally Posted By: itguy08

There is little to no MPG penalty with a modern cycling compressor system.



This is just not true.

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.

 

[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.

 

[JHZR2]

I dont know about 10%, and having just run my 240D with 67hp, I am not sure Id even say a noticeable lack of power (though an R4 compressor maybe isnt that big of a load)...

But at the end of the day there IS more load, and so there WILL be some penalty. A more efficient load is still a load...

 

[JHZR2]

Originally Posted By: pezzy669
I have actually had home HVAC techs tell me (don't know how much weight it holds) that heatpump units typically last longer than standalone a/c because the compressor is used year round. Who knows?



At least in automotive systems where there is lots of polymer hoses and o-rings, the lubricant oils serve as a barrier. Dont have it flowing around and some inherent porosity can turn into a diffusive area where refrigerant molecules can escape...

 

[cjcride]

Us shadetree types are not smarter than the guys that design this stuff for a living.[/quote]


Orville and Wilbur Wright were "shadetree" guys.

 

[Cujet]

I drive a 2011 F150 Ecoboost. It has an "AC" switch, that does absolutely nothing.

I can have it setup for "vent" only (AC off) , as it's chilly here in South Florida right now. And the AC still runs, it cools the truck and wastes gas.

If I turn off the entire system, there is no airflow, and the AC compressor won't run. I get about 1MPG more in this configuration. But, I'd much rather have some air through the vents.

Annoyed...