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Hey folks,

My wife and I go round and round about this all the time. I say it's better to turn the a/c off when you turn the car off. She never does; so it comes on immediately when the key is turned.

Problem is, I don't know exactly WHY I think it's not very healthy for the car. I must've heard it at some point.

Can anyone validate me? Or is it harmless to basically just leave the a/c on all the time?
 

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seems some time ago I read on "click and clack"'s website that before a car is turned off, you should shut off the a/c. Something about pressure being builty up in the lines. I just think it is a good idea to turn it off before you turn off the car.

recon101
 

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Having it off is also one less accessory attached and putting a load on the motor while the starter is cranking it up.

Off course to solve the problem you need to come up with a specifically ambiqiuos (spell) techie sounding prob that this guys friend, who is a mechanic, said would happen. Something like:

Starting the car with the AC on is bad. Since the thermostat isn't open the coolant lines don't work right and could rupture spraying motor oil inside the car from inside the blower box

ohhhh - sounds very dangerous /forums/images/icons/smile.gif
 
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Leaving it on , at least on our 66, just puts an extra drag on the batt and starter when starting as the a/c
clutch and blower is engaged as soon as you turn the key on. And the effect of that would show up
more in a high compression mill more than a stock setup. As far as pressure in lines etc, can't see how
that would matter any.
 

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Dreadful news for anyone looking for a techie answer why the a/c should be off when starting the car - I don't think there is one ! If it matters at all, it would only be due to the extra load on an otherwise cold engine. You probably won't find any knowledgeable answer on this ! Kind of like the "who makes the best tires" argument..
 

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How about "it puts unnecessary mechanical lag on all engine components which is especially hard on the overhead knibbler valve". /forums/images/icons/smile.gif /forums/images/icons/smile.gif
 

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I'd have to double-check this, but I don't think the clutch is engaged in the starting position, since it would run off the accessory circuit.

If you high-idle is not working right the compressor might make it harder to keep the car running until it's warmed up, but that's about it.
 

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I've also heard mechanics say to turn the a/c off before starting, but nothing about turning it off before turning the engine off. In the owner's manual of my new F-250, Ford recommends turning the a/c off before starting the engine to extend the life of the compressor and take the load off the engine. It also recommends leaving the vent open to circulate air through while parked so the vehicle "can breathe." Exact quote.
 

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Perhaps this will help you out somewhat. When the engine is running and you engage the compressor clutch it begins to spin the compressor almost immediately. This has less mechanical impact on the entire system (valves, compressor, hoses, friction points, etc.). When you have the A/C on when starting the car, the engine is not spinning freely, having not warmed up yet, and it subjects the aforementioned components to more erratic movements. The potential for damage is quite small, compared to turning it on/off at the correct times, but the potential is still there, albeit small. Then of course, there's the drag on the battery/starter as mentioned earlier, even though the circuit does not engage the clutch initially, it does come on at the tail end of the start cycle....
 

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I'm not sure what year they started doing this, but on my '97 Explorer there is a built in delay of about 2 seconds before the a/c clutch engages after the engine is started. My thoughts are that if it was important enough for Ford to build this delay in to the newer models, then it's probably a good idea to turn the a/c off when starting and stopping the engine.
 

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On most newer cars, which I am assuming you have since you marked the post O/T, the engine has to be at a certain speed for the clutch to engage,therefore when starting the car the A/C is not actually engaged, the clutch is just freewheeling. As far as shutting it off before shutting it down I don't believe there would be any more pressure than when the car is running and actually building pressure on the high side of the system. I mean, your home A/C, fridge and all cooling devices work pretty much the same way so that just doesn't make sense. Just do it the wife's way and you KNOW you will be right!!!!
 

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Like most if not all accessories, the AC is disconnected from the starting circuit, so it doesn't put strain on the engine. Same as with the radio, which you may have noticed is quiet while the car is being started but somes on after the car is running. I have the AC on constantly almost 365 days/year on my F150 with 142k miles and no AC trouble.
 
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