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Discussion Starter #1
So my parents keep insisting that if I have A/C on, drive it, then turn the car off without turning the A/C off, I'm going to "Blow the compressor". I'm a little sketchy on this whole idea. Is there are truth to it at all? I drive a 2014 Mazda3 Sport btw.
 

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No. None whatsoever. If this were true the act of the clutch engaging and disengaging (since it cycles) would be dangerous to the compressor.
 

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No problem. It is more energy efficient to turn AC off a couple minutes or so before you shut the car off, as you can capture the "cool" in the components without the compressor going those last few minutes.

Ralph
 

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ever since I had to replace my HVAC Controle module I just leave it set at 73,and dont worry I use to turn it off and on before the module went
 

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Discussion Starter #5
I figured it was a bunch of balony. Thanks for confirming though guys! I think it's even funnier though that they didn't believe me when I told them driving the car before it finishes fast idling is bad for it.
 

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I doubt that driving a car before it stops "fast idling" is generally detrimental. The normal advice is to start the car and drive off in a moderate fashion and speeds until it is fully warmed up. This allows the oil (and engine parts) to gain some heat so it can flow better and protect bearings, etc. It is usually not recommended to start a cold car and zoom off at heavy throttle, nor to let a car warm up while idling.

About the air conditioning: There are some folks who advocate turning off the compressor and letting air flow by itself before parking the car. I "think" the reason involves letting the water condensed in the system to evaporate in order to prevent a musty smell. I've never done this and have not noticed any problems. Maybe my cars have been different.

Like most other things in life, you pays your money and takes your choice.
 

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No problem with driving off when the car is in fast idle. I do it all the time. It's a waste of fuel to less it sit until the engine slows down. In the old days of carburetors, if you followed this rule, you'd be sitting in the car until the Kingdom comes. This is if you didn't drive it, the carburetor linkage would never come off the fast idle cam.

Ralph
 

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I doubt that driving a car before it stops "fast idling" is generally detrimental. The normal advice is to start the car and drive off in a moderate fashion and speeds until it is fully warmed up. This allows the oil (and engine parts) to gain some heat so it can flow better and protect bearings, etc. It is usually not recommended to start a cold car and zoom off at heavy throttle, nor to let a car warm up while idling.

About the air conditioning: There are some folks who advocate turning off the compressor and letting air flow by itself before parking the car. I "think" the reason involves letting the water condensed in the system to evaporate in order to prevent a musty smell. I've never done this and have not noticed any problems. Maybe my cars have been different.

Like most other things in life, you pays your money and takes your choice.
i can speak to the musty smell issue - the dealer even has a procedure and tool to clean/flush out the moisture to make the smell go away

i had it happen mildly when max ac / recirc air was on after most of the summer was over. turning on outside air helps, as does running the heater at max to help dry it out

mazda says this is normal - if you just leave it set to max on at all times like during a hot summer - this can end up happening
 

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The condenser has a drain, it's not going to matter. Any residual should dry out fine. I had issues with musty smell when my car was new. Once it had time to break in it's been fine.
 

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I turn off the aircon, turn off the fan, and press the fresh air button before turning off the engine, for several reason:
1. Habit mostly
2. There is less power drain (if you already have a weak battery) when starting, if the fan is off.
3. The compressor won't automatically engage when restarting (less strain on the starter and a cold engine, if the compressor is not engaged).
4. I have seen windows break from pressure build up inside of a parked vehicle in the heat of summer, if the fresh air vent is not open.

Granted, on newer vehicles, the aircon probably doesn't engage until the engine is running, but the compressor still comes on after starting and puts added strain on a cold engine. I usually ride, with the windows down, until the blue light goes off, then I turn on the aircon.

Like others have said, it won't hurt the compressor if the aircon isn't shut off before turning off the engine though.
 

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I turn off the aircon, turn off the fan, and press the fresh air button before turning off the engine, for several reason:
1. Habit mostly
2. There is less power drain (if you already have a weak battery) when starting, if the fan is off.
3. The compressor won't automatically engage when restarting (less strain on the starter and a cold engine, if the compressor is not engaged).
4. I have seen windows break from pressure build up inside of a parked vehicle in the heat of summer, if the fresh air vent is not open.

Granted, on newer vehicles, the aircon probably doesn't engage until the engine is running, but the compressor still comes on after starting and puts added strain on a cold engine. I usually ride, with the windows down, until the blue light goes off, then I turn on the aircon.

Like others have said, it won't hurt the compressor if the aircon isn't shut off before turning off the engine though.
I agree. Also living in the UK we don't need aircon most of the time. Driving off with the aircon on when you don't need it also wastes fuel.
 

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As others have said, the compressor issue is non-existent.

For moisture, here is my take...
I often turn off the A/C when I pull into my neighborhood (~60 sec before I park). I let the fan blow through the vents to warm them a bit (above the dew point). Otherwise, the cold vents will form condensation on them... potentially forming mildew/smell. It may be overkill, but I do it regardless.
 

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As others have said, the compressor issue is non-existent.

For moisture, here is my take...
I often turn off the A/C when I pull into my neighborhood (~60 sec before I park). I let the fan blow through the vents to warm them a bit (above the dew point). Otherwise, the cold vents will form condensation on them... potentially forming mildew/smell. It may be overkill, but I do it regardless.
May or may not be overkill, but know that you aren't the only one! I do the exact same procedure. After driving with the AC on, I'll turn off the AC and re-circulation but keep the fans running (or if I'm driving fast enough I don't even need the fan) to blow out any remaining cool air and allow the compressor drain to dry out faster.
 

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The only reason I do this too is because if I step out of the car after running the AC for a while, my glasses fog up. So a few moments before I reach my destination, I turn off the AC and keep the fans running to warm things up a bit.
 
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