Turning A/C on after 50 mph better for engine?

[97tbird]

A friend of mine tells me:
"...I never turn the A/c on as soon as I start the car. I wait until I start to drive, and reach about 50 mph, so that the engine has passed the high rpm areas, and have gone past o/d, and the oil has started to circulate well. only THEN i turn on the a/c...this is a lot better for the engine, and helps longevity..
turning the a/c on as soon as you start the engine is bad..."

Is there any truth to this? I know it can't harm anything to turn on the a/c after the car reahces a certain speed, but is there a real advantage?

what do you guys think?

 

[jason07-1zzfe]

No. Peak load of the compressor is about 5hp. You use more than that pulling out of the driveway.

 

[Clement]

That's what I do. Although with me, it is because I need the power for acceleration, so I turn the AC on once I'm up to speed.

I don't see how turing it on at low speeds would be bad for your engine.

 

[tom slick]

I've heard a theory that turning on your AC at higher rpms shortens your copressor's lifespan. the idea is that your compressor has to work the hardest the first time you turn it on, so not only is the compressor under it's biggest load but you are making it instantly spin at high rpm. it does not have as much load when it is cycling on during operation as the first time you turn it on.
I don't know if I actually believe that theory, but it is logical. none of my family's cars have ever had a compressor failure and nobody pays attention to when they turn the AC on.

 

[ikeepmychevytoo]

quote:

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Originally posted by motorguy222:
Isnt a compressor basically a small motor?

If so,wouldnt it be better to start it at low RPM's?

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That's exactly what I do if car sat for some time or I didn't used the AC for a while.

Both are motors but I don't see how an AC may ruin its much bigger brother. Even if it locks up big brother could chirp the belt into the fumes with smooth idle. On a '75 Olds. manual there are advised seasonal settings for the climatization. So "on" all the time is what the AC "was" designed for.

 

[motorguy222]

quote:

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Originally posted by ikeepmychevytoo:

Both are motors but I don't see how an AC may ruin its much bigger brother. Even if it locks up big brother could chirp the belt into the fumes with smooth idle. On a '75 Olds. manual there are advised seasonal settings for the climatization. So "on" all the time is what the AC "was" designed for.

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I am saying that since most engines start out at a lower RPM,would it not be good to do the same with a compressor instead of turning it on at 50 miles an hour.

No,the compressor isnt going to harm the engine,I was not stating such.

I am saying that since a compressor is basically a small motor,would it not be best to turn it on at low RPM just as any other motor?

 

[kenw]

"I've heard a theory that turning on your AC at higher rpms shortens your compressor's lifespan. "

that would be tough to determine since your ac compressor cycles on and off constantly at almost any speed.

 

[TomH]

quote:

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Originally posted by kenw:
"I've heard a theory that turning on your AC at higher rpms shortens your compressor's lifespan. "

that would be tough to determine since your ac compressor cycles on and off constantly at almost any speed.

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How very right you are! And I, for one, aren't going to sweat just to save a little wear and tear on the compressor. In my vehicles, the A/C is usually already on when I start them, except during winter.

 

[brianl703]

quote:

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Originally posted by kenw:
that would be tough to determine since your ac compressor cycles on and off constantly at almost any speed.

---

Is there any possibility that the oil in the system migrates out of the compressor as it sits idle? GM's Techlink website mentions this here but apparently it's only a concern for compressors that haven't broken-in yet.

 

[kenw]

since it only sits "off" for a few seconds (cycling), i doubt the oil has much chance to migrate anywhere.

when off for longer periods it migrates to the coolest area, wherever that may be at the time.

 

[brianl703]

I was thinking about the case where the compressor has been "off" for a long period of time (hours or days), and whether oil migration over this time would be a reason why starting it at idle would be easier on the compressor.

 

[TallPaul]

I often start the vehicle with the air conditioner in the on position. Probably a tad harder on the starter.

 

[znamya]

I think you shouldnt keep the A/C button on when you are starting the car. What I do is start the car wait 5 seconds and turn the A/C on. For me the reason for me not to turn on A/C while starting the car is from this theory. The friction has 2 components, the dynamic friction and static friction(I am not very familiar with english terminology though) the static friction keeps increasing until the pulleys move at first, then the friction goes to dynamic region which is lower, so my reasoning is, I am trying to reduce the load on the belt and pulley on the highest friction regime with not trying to load extra compressor work. FYI, this is something I remember back from my high school physics class. I think it is applicable to this case.. But I dont see why you shouldnt turn the A/C on before 55 mph. Let your friend come to atlanta, drive right at this time without A/C. He will start using the A/C before 55 mph for sure

 

[brianl703]

It's possible that newer cars may inhibit the operation of the AC compressor clutch for several seconds after the engine starts (they already do so at WOT).

 

[motorguy222]

Isnt a compressor basically a small motor?

If so,wouldnt it be better to start it at low RPM's?

 

[kanling]

Two minor reasons to wait until you are cruising on the main road before using the AC:
1. If the car's been parked in the sun and is blazing hot, you want the windows open to blow out some of the hot air anyway for a couple of minutes.
2. The AC will rob some engine power when you are starting up at traffic lights, pulling out from a side road, etc while you are on your way to the main road.

 

[kenw]

>>> the compressor clutch turns the compressor on and off at all driving (RPM) speeds. It may do this several times a minute.

You cannot control it.

TallPaul mentioned turning it off when starting, that does make it easier on the STARTER as he says. But it does nothing for the compressor.

 

[Minou]

quote:

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Originally posted by brianl703:
I was thinking about the case where the compressor has been "off" for a long period of time (hours or days), and whether oil migration over this time would be a reason why starting it at idle would be easier on the compressor.

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Exactly. Especially during the winter. I prefer to have the compressor start the first time when the engine is at a lower rpm and had time to warm up a bit or when I get out of the garage (temp above freezing), then to start the compressor on a cold -20 morning, at higher rpm with very cold oil in it.

During the summer, I start the AC as soon as I get out of the garage. It's cool down there and the AC doesn't even struggle in its lowest fan speed, even on hot and sunny days.

One more thing.
I have learned to turn off the AC a block or 2 before my destination to let go of all the water from the condensation. If not, I get a spill on my garage floor or water could remain in the system and cause odors or blockage later on.

 

['Tard]

If you run the AC on recirculate, the the humdity has been taken out of the air in the closed circuit of the cab, therefore any evaporator coil condensation and dripping has finished long before you get home.
In actuality, if you turn off the compressor and drive with the fan on for 2 blocks, you will cause condensation to build up in the system, ducts, coil, etc.
Keep AC with recirculate on for a drier system.

 

[blupupher]

I turn my A/C on when it is hot, which is most all the time here, from the time my car is started (sometimes the A/C is on when I start) and have never had a compressor problem.
The only advantage of turning it on later has already been mentioned, fuel savings, but for me whats the point. By the time I get onto a freeway and up to 50, I would have been in my car for 10 min sweating my butt off, so whats the point if I am already sweaty?