Turn the AC off before you shut the car off?

[mechanicx]

Originally Posted By: 01rangerxl
I'm just not sure what I'm wasting. Pushing the radio button and turning the a/c switch takes less effort than getting out of the truck, which is basically effortless.

Or you could just turn the key off which you are going to do anyway and everything shuts off (unless your vehicle has retained power accessory feature) and then not later have to turn your A/C and radio back on which you will probably do.

Quote:
but to me it's a matter of preference and doesn't make any difference.

That's true. I don't think it's a waste either way unless battery life is shortened or you get a moldy HVAC system. [/quote]
But that's my point. What evidence is there that battery life is shorten or that the A/C system will get moldy if you don't shut everything off before turning off the key? I don't think there is any.

 

[01rangerxl]

Originally Posted By: mechanicx

Or you could just turn the key off which you are going to do anyway and everything shuts off (unless your vehicle has retained power accessory feature) and then not later have to turn your A/C and radio back on which you will probably do.

Well like I said, I don't like starting with the fan and radio blasting. If I'm going to adjust it, may as well turn it off. The effort involved is negligible. Also, the radio faceplate gets removed when I park for any length of time.

Quote:

But that's my point. What evidence is there that battery life is shorten or that the A/C system will get moldy if you don't shut everything off before turning off the key? I don't think there is any.

Battery life I'm not sure about, but one of my notoriously lazy friends would always leave everything in his Civic turned on when he parked it. The car always smelled like mold and mildew, and always took forever to crank with that obnoxious sounding Honda starter cranking away. On the other hand, I have no mold smell and my truck cranks over immediately with a four year old Wal-Mart battery.

 

[Artem]

My 98 Toyota Camry V6 has had the AC system on for close to 15 years now and I have absolutely zero mold / smell in the car.

Of your car is suffering from mold, its because your AC system has a design flaw. A normal system takes care of itself.

I personally never turn anything off. I usually lower the radio volume to keep it from blasting upon restart but that's it.

The AC compressor engages after the engine starts, same with the fans so I don't see how its an issue or makes any difference.

You guys are all crazy and over think the whole thing waaaay too much.

Those who turn off the AC a fee minutes before arriving home to supposedly "dry" something are wasting your time. Everything still remains wet (if any)

 

[01rangerxl]

Originally Posted By: Artem

The AC compressor engages after the engine starts, same with the fans so I don't see how its an issue or makes any difference.


The fan will vary by vehicle. If mine is left on, it will start as soon as the key is turned to the on position (before start).

 

[Garak]

Originally Posted By: 01rangerxl
That's true. I don't think it's a waste either way unless battery life is shortened or you get a moldy HVAC system.


That's probably another reason I've always done it - from driving cab. The taxis tended to have radios and auxiliary lighting hooked up to work even if the ignition was off. If you didn't shut everything off before leaving, and you were gone for a length of time, you could be in for a surprise.

 

[zanzabar]

I tend to turn off the compressor before arriving at my destination too, and then shut down everything before turning off the engine. I'm in the habit of 15 seconds of idle before shutting the engine down from my turbo cars though.

But then again, I turn off the compressor when driving up a hill sometimes to save a few 0.001 mpgs and then turn it back on when going downhill since the extra draw will help with engine braking.

 

[lexus114]

Originally Posted By: zanzabar
I tend to turn off the compressor before arriving at my destination too, and then shut down everything before turning off the engine. I'm in the habit of 15 seconds of idle before shutting the engine down from my turbo cars though.

But then again, I turn off the compressor when driving up a hill sometimes to save a few 0.001 mpgs and then turn it back on when going downhill since the extra draw will help with engine braking.

Ooooookay.

 

[TFB1]

Originally Posted By: zanzabar

But then again, I turn off the compressor when driving up a hill sometimes to save a few 0.001 mpgs and then turn it back on when going downhill since the extra draw will help with engine braking.

I just floor the throttle which automatically cuts out the compressor... I don't buy my vehicles based on fuel economy...

 

[zanzabar]

Those little instantaneous fuel mpg meters really do have an effect on you!

 

[ltslimjim]

Better MPG steady speed without AC use...engine braking if you need if, maybe but might need more engine braking for DFCO to kick in with A/C on due to increased fuel consumption/air intake for the cycling of the compressor anyway.

 

[CharBaby]

Originally Posted By: buster
My wife never turns the AC off before shutting the car off. So when you start the car up the next day, it immediately goes on. Is that bad?


Ya know, over 35+ yrs with the same beautiful girl, I have stopped trying to get my wife to not do some things with our vehicles.

1)Stop starting the car, and before the rev even comes down from the initial startup, the tranny is in gear.

2)Stop slamming the doors.

3)Stop starting the engine just to move the car 2 ft.

4)Stop letting the engine warm up in the winter time for longer than your trip is going to be(15 min warmup/5 min drive).

I've stopped trying to get her to stop! I've never had problems with my cars because of what she is doing. Other issues maybe but, not her fault. Engines never failed and the doors never fell off!

 

[DaHen]

Originally Posted By: Char Baby

I've stopped trying to get her to stop! I've never had problems with my cars because of what she is doing. Other issues maybe but, not her fault. Engines never failed and the doors never fell off!


Well, at least she never told you about the time when the engine failed and the time when the door fell off. lol.

 

[Jim Spahr]

Those of you who said: 'I never shut off any accessories before I turn off the ignition', need to rethink that. I am speaking of the windshield wipers. They need to be shut off and allowed to park before turning off the ignition. If you don't, the next time someone goes out to restart the engine, the wipers will scratch the dry windshield. If it is winter and the weather is cold and wet, the wipers may be frozen to the windshield the next morning and the first start may tear the w/s wiper blades. The other reasons have already been stated above: 1./ Reduced strain on the battery during starting. and 2./ Reduce mold build up in the evaporator during the summer months.

 

[440Magnum]

Originally Posted By: buster
My wife never turns the AC off before shutting the car off. So when you start the car up the next day, it immediately goes on. Is that bad?

Not an issue at all on modern cars since the AC is under the control of the engine management system. Have someone crank it up with the AC on and watch the AC clutch. It won't even kick in until the engine has started and the idle speed has started to settle back down to normal.

 

[440Magnum]

Originally Posted By: JHZR2
Bigger concern is every extra ampere drawn from the fan (which IME does come on right away on all cars), causing more voltage drop.

To me the bigger question is of mold and how to prevent it. To me that is to turn off the AC with fan blowing. Thing is, on humid days, this means the interior of the car gets damp, which could mean mold elsewhere in time.


To your first point: The two newest cars in my "fleet" (the 05 PT and the 08 Ram) actually run their electric fans for about a minute when you start the engine EVEN WITH THE AC OFF and the engine dead cold in winter. My assumption is that they do that to clear the engine bay of any accumulated fuel vapors, but that's just a guess... anyone know the real reason?

To the mold issue: I've noticed that the AC cores tend to get a moldy smell WORSE if I try to run the fan for a while with the AC off before I shut the car down. If I shut it down with the AC running and the core cold, it generally doesn't smell when I start it up again. My guess here is that blowing warm air over the core so that it warms up while still moist just plants more mold spores on it, whereas shutting it down with it ice cold and then letting it slowly warm with no air flowing over it minimizes the crop of mold.

 

[Jim Spahr]

440 Mag asked:
To your first point: The two newest cars in my "fleet" (the 05 PT and the 08 Ram) actually run their electric fans for about a minute when you start the engine EVEN WITH THE AC OFF and the engine dead cold in winter. My assumption is that they do that to clear the engine bay of any accumulated fuel vapors, but that's just a guess... anyone know the real reason?
Sam Memmolo in his weekly radio show 'Sam's Garage' said that in the summer time, he always shuts off his a/c when stopping. Then when he restarts his truck, he first turns on the fan only to blow out the warm air built up in the ducting while stopped. Then he cuts on the A/C to blow cold air. ( I am paraphrasing Mr. Memmolo here!) It sounds like he is manually doing what your PT and Ram are programmed to do automatically. The idea is to not overtax the A/C system with dealing with the warm air trapped in the ducts.

 

[SwampSurvivor]

I always let my car run for 30 seconds or so before turning it off. Force of habit I guess?

The AC gets turned off when I'm pulling into the driveway/parking lot. That way the fan can run and cool it down a bit.

 

[440Magnum]

Originally Posted By: Jim Spahr
440 Mag asked:
To your first point: The two newest cars in my "fleet" (the 05 PT and the 08 Ram) actually run their electric fans for about a minute when you start the engine EVEN WITH THE AC OFF and the engine dead cold in winter. My assumption is that they do that to clear the engine bay of any accumulated fuel vapors, but that's just a guess... anyone know the real reason?
Sam Memmolo in his weekly radio show 'Sam's Garage' said that in the summer time, he always shuts off his a/c when stopping. Then when he restarts his truck, he first turns on the fan only to blow out the warm air built up in the ducting while stopped. Then he cuts on the A/C to blow cold air. ( I am paraphrasing Mr. Memmolo here!) It sounds like he is manually doing what your PT and Ram are programmed to do automatically. The idea is to not overtax the A/C system with dealing with the warm air trapped in the ducts.


I was actually talking about the under-hood electric fans, not the interior fans.

Also here's one for the "did you know" file... Is it more "taxing" on the air conditioning system when the interior of the car is really, really hot (and you're on "recirculate"), or is it more taxing when the interior is cold and you have the AC on "recirc"? Assume that the exterior temperature of the air flowing across the condensor is the same in either case.

Its actually just slightly harder on the system when the interior is cool, because the pressure differential across the compressor is larger. When the evaporator is hot, the refrigerant boils to gas completely and the suction pressure is higher. The high-side pressure remains roughly the same because its fixed by the outdoor temperature.

 

[SteveSRT8]

There's a lot of reasons for the fans to run.

On my car they do the "burst" at startup but many other things trigger them. They cycle for temp of course, but also trans temp and AC high side pressure.

I have never heard a specific reason for the startup behavior. But it only happens in HOT weather when the car was parked with the AC on at shutoff. So I imagine it was for the ac condenser.

 

[CharBaby]

Originally Posted By: DaHen
Originally Posted By: Char Baby

I've stopped trying to get her to stop! I've never had problems with my cars because of what she is doing. Other issues maybe but, not her fault. Engines never failed and the doors never fell off!


Well, at least she never told you about the time when the engine failed and the time when the door fell off. lol.

I was always wondering why that paint never really matched well and the engine stumbled a bit! LOL :0