A/C and engine start-up

[Mike]

I was always told as a teenager by my old man to turn off the A/C before
shutting off the engine, and more importantly to make sure it was off before
cranking it up to prevent damage (to what?). Can anyone confirm this or is
it rumor? I could perhaps see the logic at start-up due to the extra load
on the starter, but really, does it make a beans difference?

Mike

 

[Jim Stewart]

I was always told as a teenager by my old man to turn off the A/C before
shutting off the engine, and more importantly to make sure it was off before
cranking it up to prevent damage (to what?). Can anyone confirm this or is
it rumor? I could perhaps see the logic at start-up due to the extra load
on the starter, but really, does it make a beans difference?

I think it's one of those things that probably
made sense in it's time but doesn't matter any
more. I've never worried about it and never
had a problem.

I personally find it annoying that my wife relies
on the ignition switch to turn the headlights on
and off. My old man said to never start the car
with them on.

 

[Ed P]

I think it's one of those things that probably
made sense in it's time but doesn't matter any
more. I've never worried about it and never
had a problem.

I personally find it annoying that my wife relies
on the ignition switch to turn the headlights on
and off. My old man said to never start the car
with them on.

Mike,

An additional -- perhaps minor consideration -- is that in some
circumstances the moisture that is removed from the air as part of the
cooling process can lead to mildew or fungus growth in the evaporator
case, with attendant bad odors. Shutting off the A/C but continuing to
run the blower fan for a few minutes before shutting the car off
(especially when parking for several hours) can reduce the chance of the
mildew or fungus growing.


Ed P

 

[Victor Roberts]

I personally find it annoying that my wife relies
on the ignition switch to turn the headlights on
and off. My old man said to never start the car
with them on.

I do this all the time on my 97 OB. It provides a "running light"
function that the car would otherwise not have. On many cars the
headlamps are turned off automatically when the starter motor is on -
not sure if that happens on my OB.

 

[etienne]

The major benefit I can see with leaving off the AC at startup is to
keep the load off the battery after startup. All cars today disable the
AC during startup but as soon as you release the key the AC will kick
on and therefore put a heavy load on the battery...therefore give you
electrical system a break...

 

[Victor Roberts]

The major benefit I can see with leaving off the AC at startup is to
keep the load off the battery after startup. All cars today disable the
AC during startup but as soon as you release the key the AC will kick
on and therefore put a heavy load on the battery...therefore give you
electrical system a break...

How does the AC load the battery? There is an electrically actuated
clutch, but the compressor is driven by the engine.

 

[Mike]

the battery runs the starter, which turns the engine which now has extra
load on it b/c of the A/C pump.

 

[etienne]

Battery/Generator/Alternator produce electricity. While the engine is
idling after starting, the alternator does not generate enough power to
recover the loss from starting the engine, also does not generate
enough power to run everything:
1. AC requires a electrically actuated clutch, that actuation is a
solenoid that uses a lot of power, that solenoid continues to draw
power as long as the clutch is actuated!!!!!!!!!!
2. Dual electric fans on the radiator are running to draw air through
the radiator.
3. Your inside fan is running as well to cool the interior of the car.
This list does not include stuff like fuel system, ECU, etc........

Therefore give the battery a break!!!!!!

 

[ed]

Not only the clutch, but the radiator fan and the heater system fan are
activated as well.