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This may seem like a very dumb question but should the AC be on when the heat is on? I know that when I turn on my defrosters the AC automatically kicks on, but I always shut it off and leave the defrosters on.

Is it bad to have AC on when the heat is on?
 

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Naw not bad... in fact the AC should be ON often to help lubricate the system.

I don't remember at what temp but the AC will not operate below some temp.... 24°F?????

By being on it will help remove moisture from the enterior of the MO. Slight decrease in gas millage. I typically leave mine off but do try to remember to excercise it at least once every 1-2 weeks.
 

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Having the AC on (meaning the button is lighted) does not necessarily mean that the air is being cooled down as it goes through the system.

In fact, I've noticed that the compressor kicks in less frequently when the heater is on compared to during the warmer months when I actually need the air to be cooled.

But it DOES keep the moisture down inside the vehicle, which helps for windows fogging up and reducing that stale-mildewy smell you often get in the wintertime. In my last car I started leaving the AC on all the time in the winter for exactly those reasons, and it really helped.

The change in gas mileage should be minimal. I would go as far as to say insignificant. Especially if the compressor is kicking on infrequently, like I believe it is. But I wonder more about how long the AC system will last if it's in constant use? Might that cause something to wear out sooner, or does it really help to "lube" the system so that it lasts longer?
 

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Corin said:
...But I wonder more about how long the AC system will last if it's in constant use? Might that cause something to wear out sooner, or does it really help to "lube" the system so that it lasts longer?
I don't know about the lube as I belive the oil in the system is mixed with the refrigerant and spread throughout the system, coating the insides so unless the system has air or moisture in it (witch is very doubtful if it is running properly) I do not think it is necessary to run it just for the sake of lubrication.

The only "wearable" part of the AC system is the compressor which has an electromagnetic clutch assemply, a few bearings, and a valvebody. The more you use it, the more it wears, but these are usually desinged to last the lifetime of the vehicle so I would not really worry about using them too much.
 

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There really is no need to periodically cycle the A/C to "lube" the system. Do you cycle your home's A/C in the winter to lube it? The A/C system is a closed system. The lines have been purged of air and moisture prior to being filled with refrigerant and oil.

Corin is correct when he says the A/C compressor is not necessarily running just because the A/C light is on. That just means the A/C is available if the conditions warrant.

IMHO it is best to leave the A/C "on" in the winter. It doesn't run that often, but when it does it makes a difference to the moisture (comfort) level in the car.

-njjoe
 

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njjoe said:


Corin is correct when he says the A/C compressor is not necessarily running just because the A/C light is on. That just means the A/C is available if the conditions warrant.

-njjoe
Not necessarilly true... the system will trun the compressor to maintain AC system pressure. It might be less in the cooler months but it is still cycling.

Regarding lubing the system, at least with older systems and perhaps the new ones as well the system circulates the R42/freon or whatever they use these days which help to lube the fittings/seals.
 

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Gonzo said:


Not necessarilly true... the system will trun the compressor to maintain AC system pressure. It might be less in the cooler months but it is still cycling.

Regarding lubing the system, at least with older systems and perhaps the new ones as well the system circulates the R42/freon or whatever they use these days which help to lube the fittings/seals.
Gonzo-

The A/C compressor does not cycle to maintain system pressure. There is no need for it, it is a closed system. In fact, it is easier to start the compressor after the high-pressure side had bled down. That is why room air conditioners need to wait a minute or so before the compressor can be restarted.

5.03 ounces of oil circulates within the refrigerant (R-134a) loop to lubricate the compressor.

-njjoe
 

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It's an engine.
It needs to be run.
Just like your regular engine that also has the moving parts lubricated, the lubricant runs down, following the law of gravity, leaving the parts not lubricated for the next start.


From
http://www.edmunds.com/ownership/techcenter/articles/46869/article.html

" Second, if you live in a place with a cold climate, it might not make much sense to run the A/C during the winter months, but many shop technicians recommend running your A/C system regularly, because it contains a light mineral oil in the refrigerant to keep the compressor properly lubricated. The general rule of thumb is 10 minutes per month."

I always ran my manual AC for 10 minutes a week.
I haven't had an AC unit go "bad" in many, many years. The last one I can remember was on an 86 Dodge turbo car. It developed a leak and it ran without refrigerant (And obviously without oil) for awhile. Goodbye compressor.

Seems like a pointless argument as it is
A- easy to do
B- Can't hurt
and
C- might help

With the Murano I leave the Auto on all the time.
I paid for an auto system and I am going to use an auto system. :)

Homer
 

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njjoe said:


Gonzo-

The A/C compressor does not cycle to maintain system pressure. There is no need for it, it is a closed system. In fact, it is easier to start the compressor after the high-pressure side had bled down. That is why room air conditioners need to wait a minute or so before the compressor can be restarted.

5.03 ounces of oil circulates within the refrigerant (R-134a) loop to lubricate the compressor.

-njjoe
Really I thought the pressure does change... wouldn't it have to as the system "removes heat" and thus changes temp and pressure? Why does it cycle then?
 

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Gonzo said:


Really I thought the pressure does change... wouldn't it have to as the system "removes heat" and thus changes temp and pressure? Why does it cycle then?
Yes, you are right. Changes in pressure and physical state (gas <--> liquid) of the refrigerant are what is behind the transfer of heat from the evaporator inside the car to the condenser outside the car.

I had misinterpreted your statement to mean the A/C compressor would turn on periodically to maintain a minimum pressure in the system, regardless of whether cooling was called for. Which wouldn't be the case. Sorry about that, Gonzo.

-njjoe
 

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No worries just wanted to be sure I had the correct idea. However regardless of wether it is called for the pressure will change... the system is in the engine compartment. The pressure will change. If you could run the system with the interior fan off the compressor would still cycle.

No boot strapping here.
 
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