A/C and the starting / turning off the vehicle

[squarecut1]

The A/C should be off when you start a vehicle. Thus before turning off the engine, you should turn off the A/C

Is this an old wives' tale or is there merit to it? Thanks

 

[jlee]

My AC is always on. One truck has 279k and the other has 210k. I wouldn't worry about it too much.

 

[Jimzz]

Should not really make any real difference at least with current cars. There are safety switch's on the AC system if it has to much or little pressure and will shut off.

 

[JulesMaximus]

Mine runs off electricity anyway and isn't driven by the engine so it doesn't matter at all.

 

[LTC8K6]

Auto climate control on the Jeep so I don't worry about it.

Most car computers do not power up the A/C clutch until the engine is running, so the compressor is not turning during cranking.

My 1995 Taurus was that way.

 

[kitatech]

A/Cs start a second or so after the engine's running...I like to have it run to "load" the initial idle and keep it "in check".

 

[LTC8K6]

Mine runs off electricity anyway and isn't driven by the engine so it doesn't matter at all.

Well, not directly...

 

[LTC8K6]

A/Cs start a second or so after the engine's running...I like to have it run to "load" the initial idle and keep it "in check".

My old Taurus and my 2008 Jeep were both about 5 seconds.

 

[Wingznut]

VERY OLD wives' tale.

 

[Railgun]

You can also run down the 1/4 with it on as well and it will not affect anything/hurt performance.

 

[bruceb]

Makes no difference unless you have a very weak battery.

 

[LTC8K6]

Makes no difference unless you have a very weak battery.

I think it does, actually. The compressor can take several horsepower to turn.

I always wondered if they didn't want the compressor turning that slow anyway.

 

[kitatech]

Makes no difference unless you have a very weak battery.

I think it does, actually. The compressor can take several horsepower to turn.

No....it doesn't,

I guess you missed the posted fact that the compressor doesn't go on until AFTER the engine has started.

 

[LTC8K6]

No....it doesn't,

I guess you missed the posted fact that the compressor doesn't go on until AFTER the engine has started.

Missed it...

I posted it...post #5.

I was talking about the idea that the compressor could be on when the engine starts. If that were the case, I speculated that it could make a difference due to the HP required to turn it.

The weak battery suggestion was clearly about the compressor clutch possibly being engaged during cranking, otherwise why mention the battery?

 

[Wingznut]

Perhaps there are some... But I'm not aware of any modern car that has the compressor engaged while cranking.

Same with wide open throttle (or high rpm) situations... The compressor disengages.

 

[master_shake_]

never seen a car that has the a/c on start up, typically the accesories drop out until the car is back in the run position.

even on cars as old as 1980's

 

[LTC8K6]

Yeah, the clutch would have to fail where it was stuck engaged.

 

[master_shake_]

Yeah, the clutch would have to fail where it was stuck engaged.

considering its a magnet that engages it that would be quite the failure :awe:

 

[LTC8K6]

considering its a magnet that engages it that would be quite the failure :awe:

Stuck relay, bad sensor, rust/corrosion, dead animal remains... :biggrin:

 

[soccerballtux]

Mine runs off electricity anyway and isn't driven by the engine so it doesn't matter at all.

what car is this, and that's gotta do wonders for the gas milage

 

[_Rick_]

You can also run down the 1/4 with it on as well and it will not affect anything/hurt performance.

Wouldn't be so sure of that.
Sure, if you're making 400HP+ 10HP more or less don't matter, but with smaller engines the compressor still takes a few kW off the engine. If you've got less than a 100 of those, you'll be feeling the loss.

 

[SpatiallyAware]

It has nothing to do with engine load or wear.

Up until the last 20-30 years vehicles with A/C didn't have that great of condensate drains.

If you didn't turn the AC off for the last couple miles to dry it out you would end up with a mildew smell in your evaporator coils/box.

 

[michal1980]

Wouldn't be so sure of that.
Sure, if you're making 400HP+ 10HP more or less don't matter, but with smaller engines the compressor still takes a few kW off the engine. If you've got less than a 100 of those, you'll be feeling the loss.

under wot most/all recent cars disable the ac.

 

[LTC8K6]

Most modern cars disable extra loads when you move the throttle quickly to call for rapid acceleration. You don't need to hit WOT.

 

[Ben90]

While I haven't owned the most modern cars (95 del sol, 00 eclipse, 87 fiero), none of them shut off the compressor on WOT.