Should I start my car with the A/C off?

[DJL 232]

I need to explain why this idea is bunk. Anyone have any sources? I have a bunch of online sources but I'm looking for something directly from a mechanic or car manufacturer.

The question is purely whether there is any adverse affect to the car if it's on during startup. Obviously if you were not going to use it after startup then it's a cycle it didn't need to go through.

I'm sure there are exceptions but most cars will disengage everything but the engine when you turn the key to start the engine. They then come back on when the key springs back to the on position. This is the same as if it were off and then after you started the engine you turned it on.

"I encourage all awesome dangerous behavior." - Jeffro Fincher

[wmw999 2,121]

From Car Talk. They aren't just mechanics, they're MIT-educated mechanics.

Wendy W.

There is nothing more dangerous than breaking a basic safety rule and getting away with it. It removes fear of the consequences and builds false confidence. (tbrown)

[DJL 232]

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From Car Talk. They aren't just mechanics, they're MIT-educated mechanics.

Wendy W.

MIT has a Masters in Auto Repair? I listen to them on the radio, just have always tried to figure out that connection.

"I encourage all awesome dangerous behavior." - Jeffro Fincher

[Belgian_Draft 0]

In addition to the link Wendy posted, the AC in your car cycles on and off even when you have it turned off. There are several reasons for this, including keeping the compressor lubricated. Even if the A/C was cycled again every time you started the engine, the total number of extra cycles it would go through in the cars life would be insignificant when compared to the number it goes through anyway.

Your post does bring to mind something else. The last two vehicles I have owned I purchased new. I have driven them a total of well over 350,000 miles in the last 8 years without any problem with the A/C. Before that it seemed it was a yearly event keeping the A/C working through the summer. Kudos to the manufacturers for the much improved reliability.

HAMMER:
Originally employed as a weapon of war, the hammer nowadays is used as a
kind of divining rod to locate the most expensive parts adjacent the
object we are trying to hit.

[CSpenceFLY 1]

Mine stays on all the time and I use the temp control.

[popsjumper 2]

...from October to March, I'd say yes.

My reality and yours are quite different.
I think we're all Bozos on this bus.
Falcon5232, SCS8170, SCSA353, POPS9398, DS239

[JohnRich 4]

I don't know if the effect on extra wear is significant or not.

But I just look at it from a practical standpoint. There's no sense in causing extra wear on something that you're not going to use, or extra load on an engine that could be saving more gas.

Also, you can think of the mechanical life of an assembly as finite - it's only going to perform properly for a certain number of cycles, or amount of time, before it will need repair. Kind of like the "TBO" (time between overhaul) cycles on aircraft engines. In that case, experience has shown that at a certain point, failures start to occur, therefore it's prudent to overhaul them before they get to that point.
Just like replacing the lines on your canopy at 500 jumps instead of waiting for some of them to start breaking.

Given that philosophy, then anything you can do to reduce the wear time, will prolong the interval before the next expensive maintenance.

This is good for me, because I keep my cars until they die. On the other hand, if you buy new cars, and regularly trade them in after just a year or two, then none of this matters - whatever accumulative wear you put on it is not going cause a problem while you own it, but will be passed on to be someone else's problem further down the road.

[DJL 232]

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...from October to March, I'd say yes.

Interesting enough the full conversation is heating also. I often get into the car and start driving only to realize that the windows are icing up from the inside because the heat isn't on. But the SO's father taught his daughter well and someone with a degree in mechanical engineering and working in the field of HVAC design COULDN'T be right.

"I encourage all awesome dangerous behavior." - Jeffro Fincher

[DJL 232]

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But I just look at it from a practical standpoint. There's no sense in causing extra wear on something that you're not going to use, or extra load on an engine that could be saving more gas.

I see what you're saying but I have the heat on when it's cold and the AC on when it's hot. The fan is usually on. What do you think about Belgian Draft's post that it cycles on and off anyway?

"I encourage all awesome dangerous behavior." - Jeffro Fincher

[BikerBabe 0]

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Quote

From Car Talk. They aren't just mechanics, they're MIT-educated mechanics.

Wendy W.

MIT has a Masters in Auto Repair? I listen to them on the radio, just have always tried to figure out that connection.

no, they are mechanical engineers. MIT certainly has degrees in that.

Never meddle in the affairs of dragons, for you are crunchy and taste good with ketchup!

[wmw999 2,121]

Actually Ray has a degree in general studies.

I leave the heat off when I turn the car off, but that's mainly because I want the engine to get to something more than freezing cold before it starts putting air out at me.

Wendy W.

There is nothing more dangerous than breaking a basic safety rule and getting away with it. It removes fear of the consequences and builds false confidence. (tbrown)

[normiss 622]

The ac compressor isn't active during start-up, no wear possible.
Heating is taken from water circulation which IS happening whenever the engine is running...so no added load, nor can you "stop" it per se.

[DJL 232]

And right there is the practical side of it. I do the same thing and when it's REALLY muggy and hot out I leave the system off so I don't get a face full of dank hot air. I drive with the windows down to get that first bit out and then start bringing up the AC.

People who drive pristine or collector cars with nice or delicate interiors will usually leave the AC off before they park it and let the car air out so there's no condensation.

"I encourage all awesome dangerous behavior." - Jeffro Fincher

[normiss 622]

You did make a nice point there...when the a/c is left on, if you have the vents set for outside...then you are exposed to the atmosphere, correct?
Turning it off would cause the vacuum systems to pull the vent closed I believe.

[DJL 232]

It's really because there's usually a lot of warm, if not hot, water on the cooling coil from the last time you drove. It evaporates quickly into the airstream.

"I encourage all awesome dangerous behavior." - Jeffro Fincher

[Rookie120 0]

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MIT has a Masters in Auto Repair?

Don't know. But there degree is in automotive engineering. Which I think MIT would be one of the best places to go so Ithink they know what they are talking about. They are fun to listen to on the weekend.

If you find yourself in a fair fight, your tactics suck!

[regulator 0]

Dude come to south texas and you will need that AC running 24/7. During nights in the summer it can get up to 90 degrees easy.

[JohnMitchell 14]

Just make sure it's in neutral (or park, if you have a slush-a-matic transmission).

Yes, much Kudos to the manufacturers for the improvement in cars overall. 100K until you change the plugs? Crappy old carburetors a thing of the past? Tight handling rack and pinon on even the econo-boxes? I'm nostalgic for the old muscle cars, but I really don't miss them too much, except when I try to pass someone on a two lane highway.

[JohnRich 4]

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But I just look at it from a practical standpoint. There's no sense in causing extra wear on something that you're not going to use, or extra load on an engine that could be saving more gas.

I see what you're saying... What do you think about Belgian Draft's post that it cycles on and off anyway?

I don't know much about car engines any more. In the old days, we would just manually turn the AC on every once in a while in the winter to keep the compressor lubricated. Just like we turned the heater on in summer to keep any radiator fluid from getting rusty from laying inside the heater box without circulation.

If that happens automatically now, I don't know how frequently that occurs. I imagine it would be less than what would happen if it was actually being used to produce cooling. So there still might be some savings on wear and tear by leaving it off when it's not needed.

[DeNReN 0]

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Should I start my car with the A/C off?

I does not matter if the A/C is on or off when starting a modern automobile. it will have no adverse effects on any systems unless there is already a problem developing that could be affected by the additional load on the engine and electrical system...

Most modern automobiles equiped with A/C will run the A/C when the front defrost or floor/defrost modes are selected....this serves 2 functions...it keeps the A/C compressor and possible "H" valves moving and A/C also acts as a dehumidifier...dry air clears windows much better then air with a high humidity.

[SuFantasma 0]

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From Car Talk. They aren't just mechanics, they're MIT-educated mechanics.

Wendy W.

Wow, that's a powerful statement "MIT-Educated Mechanics".... is that the same as Unemployed Professors, Misfit Engineers or Government Geniouses?

We will need a new thread for MIT-Educated AFF Instructors... THAT would be the subject of celebration and would deserve a new Incidents thread dealing with Quantum Skydiving Physics and the Risks of Missing the Spot over a black hole.

Y yo, pa' vivir con miedo, prefiero morir sonriendo, con el recuerdo vivo".
- Ruben Blades, "Adan Garcia"

[wmw999 2,121]

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MIT-Educated AFF Instructors

Ummm -- you do realize we have one, don't you?

Wendy W.

There is nothing more dangerous than breaking a basic safety rule and getting away with it. It removes fear of the consequences and builds false confidence. (tbrown)

[Rookie120 0]

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Ummm -- you do realize we have one, don't you?

Billvon or Kallend?

If you find yourself in a fair fight, your tactics suck!

[wmw999 2,121]

Billvon (hence the green). I don't think Kallend is an instructor, and he went to school in England.

Wendy W.

There is nothing more dangerous than breaking a basic safety rule and getting away with it. It removes fear of the consequences and builds false confidence. (tbrown)

[el6uapo 0]

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I need to explain why this idea is bunk. Anyone have any sources? I have a bunch of online sources but I'm looking for something directly from a mechanic or car manufacturer.

The question is purely whether there is any adverse affect to the car if it's on during startup. Obviously if you were not going to use it after startup then it's a cycle it didn't need to go through.

I'm sure there are exceptions but most cars will disengage everything but the engine when you turn the key to start the engine. They then come back on when the key springs back to the on position. This is the same as if it were off and then after you started the engine you turned it on.

I always thought that the A/C is powered by the engine. If the A/C is on when the engine starts doesn't it put an additional, immediate load on the engine? You can hear the engine revs change when you turn A/C on.

So, when you first start your engine the oil is thicker than when it is warm. More load on the engine when the oil is thick, the harder it is on the entire system. This is why there are different oil viscosities for winter and summer driving.

Conclusion, it is bad to turn A/C on until you give the oil in the car a second to warm up. This follows the same idea that not giving your car any time to warm up in the winter is bad.

This is just what I thought...