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Old 12th April 2009, 21:15   #1
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Default Can we switch ON AC, while engine starts?

I am having an doubt regarding air con, to save fuel, i will switch off the engine at red signal and the car was in AC 'on' mode before shutting engine,

when i again switch on the engine , do i need to switch off the AC before firing engine? or There is no problem even if air con switch is in ON position when i start the engine?

Does this affect compressor?
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Old 12th April 2009, 21:21   #2
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rajiv from what i know, you should not keep the compressor on when the engine is not running. puts a lot of load on the battery and compressor. avoid doing it!
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Old 12th April 2009, 21:42   #3
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Quote:
Originally Posted by white_vdi View Post
rajiv from what i know, you should not keep the compressor on when the engine is not running.
+ 1 to what white_vdi has said. The extra load on the battery will also shorten its life considerably.

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Old 12th April 2009, 21:43   #4
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The compressor does not get on when the engine is off.
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Old 12th April 2009, 21:54   #5
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Quote:
Originally Posted by bblost View Post
The compressor does not get on when the engine is off.
It does.

Don't switch on the A/C with the engine off! Else, you will have a dead battery!

Even if the compressor does not get on, the blower will drain the battery!
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Old 12th April 2009, 21:57   #6
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Quote:
Originally Posted by bblost View Post
The compressor does not get on when the engine is off.
From what I understood, he is referring to cranking the engine with the compressor (AC switch) turned on. This cranking is bound to put a strain on the engine and battery.

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Old 12th April 2009, 22:01   #7
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Guys,

When the engine is off... Compressor is not running.. so a/c button on/off makes no difference. ONLY the blower is running and of course its battery operated.

It would be really stupid to each time hit the a/c switch at lights. There would some more better things to do.

However, I would recommend turning off a/c while starting up in the morning and shutting down in the evening.
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Old 12th April 2009, 22:05   #8
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How can the a/c compressor run with the engine off? It doesn't run on battery power alone. The increase in engine rpm and drop in available power when the compressor switches on is obvious in any car.

rajivanoj, since the car is capable of being switched on with the a/c switch on, it's not fatal to either the engine or the a/c. (The same logic applies to cellphone use on aeroplanes-- if it REALLY affected the aircraft navigational systems, airlines would make jolly well certain of no phones on planes, instead of merely asking you to turn them off.)

However, I'm sure it does somehow "strain" the engine and battery, although the specifics elude me. Certainly you shouldn't start with the a/c on when the engine is cold, or before it's reached optimal operating temperatures. Bottom line-- don't start with the a/c on if you can help it.

And you certainly can help it, by making it a habit, even in traffic. I always make it a point to turn off the a/c before switching off the ignition, so that I don't forget to turn it off before starting the next time. In fact my sequence after stopping at the destination is handbrake - neutral - kill a/c - kill lights - kill engine.
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Old 12th April 2009, 22:09   #9
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it will not put any load on the car battery when the AC switch is on and the engine is off.
but i am not sure about this,will it put load on the electrics when you on the engine because compressor takes some time to start say about 5/6 sec .

my advice,when ever you start the car check that every thing is in off mode ac/ice/light.
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Old 12th April 2009, 22:32   #10
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Most Car Manuals (if not all) mention that everything should be "off" including your headlights, AC , ICE etc when you crank the engine . Period !
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Old 12th April 2009, 22:57   #11
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Quote:
Originally Posted by taranonline View Post
It would be really stupid to each time hit the a/c switch at lights. There would some more better things to do.
Poor reasoning, IMHO. What better to do while driving than drive properly, taking as much care of your vehicle as possible? How hard is it to hit the a/c switch with your left hand?
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Old 13th April 2009, 00:10   #12
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As far as i know in some cars when ac is running and we switch off the engine without switching off AC , the next time we start the engine the Ac Compressor is not connected till the car starts though the blower does run even while cranking .
In my maruti 800 if i donot switch off the ac and turn off then when cranking it puts strain on starter motor .But in my freinds Estilo Vxi and another Santro Xo the irrespective of the Ac button when i crank the ac will not start till the car starts even if the AC button was on from start.
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Old 13th April 2009, 00:38   #13
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I never switch off the engine at signals. I always crank the engine with the A/C, music system on. Have been following this practice in the Indica since 35000 km (~25 months). The OEM battery lasted 39 months / 60000 km (thanks to a busted regulator). The replacement Amaron is running fine after 34 months / 37000 km. Have also been following the same practice in the Safari from day 1 (26 months / 62000 km so far).

Go figure

Last edited by hrag : 13th April 2009 at 00:41.
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Old 13th April 2009, 00:39   #14
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Quote:
Originally Posted by taranonline View Post
When the engine is off... Compressor is not running.. so a/c button on/off makes no difference.
Quote:
Originally Posted by Perakath View Post
How can the a/c compressor run with the engine off?
...it's not fatal to either the engine or the a/c.
Quote:
Originally Posted by karankapoor View Post
it will not put any load on the car battery when the AC switch is on and the engine is off.
With the AC switch AND blower switch on, even when the engine is off, the battery keeps running two things which drain a good amount of power - the auxiliary cooling fan behind the radiator and the AC compressor clutch. This extra load on the battery may not allow the battery to provide full current to the starter while cranking, and unnecessarily strains the battery. Plus, the load of the AC compressor on the starter motor when cranking, also strains the starter itself.

Hope this helps.

Last edited by SS-Traveller : 13th April 2009 at 00:40.
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Old 13th April 2009, 00:53   #15
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Quote:
Originally Posted by SS-Traveller View Post
With the AC switch AND blower switch on, even when the engine is off, the battery keeps running two things which drain a good amount of power - the auxiliary cooling fan behind the radiator and the AC compressor clutch. This extra load on the battery may not allow the battery to provide full current to the starter while cranking, and unnecessarily strains the battery. Plus, the load of the AC compressor on the starter motor when cranking, also strains the starter itself.

Hope this helps.
i think we are only talking about the AC switch,not the blower.
auxiliary fan comes in when the engine is hot.
and when the blower is off and the AC switch is on how will compressor get's the current
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