[Jaggu]

If you can switch off the compressor switch good, though no major harms since the modern day car circuit will cut off the ac compressor, blower etc before the engine fires up. They will be switched ON after a delay of 1-2 secs automatically after the engine is running.

Regular usage (like signals and short parking) i dont use the ac comp switch (leave it ON always) and just manage it with the blower switch , which will take care of the compressor also in Maruti vehicles. Only in the morning and cold starts, i run with blower ON for the engine to warm up a bit and then switch the compressor separately.

Technically no harm but being a car lover, definitely recommended to wait for few secs for engine to catch its breath

[Atlblkz06]

You guys are so high strung about the small stuff, you're going to die of hypertension before anything happens to your cars...lol

I don't think this will have any impact on your car's longevity. Enjoy the journey!

There is a lot of misinformation on the first page (and good information later on).
* The A/C compressor does not run when your engine is off.
* If your turn off your car at a light, the compressor is off, but the blower is on. You will feel some residual A/C effect for a minute tops before it starts warming up.
* Modern cars may disengage the A/C clutch when cranking - I don't know if mine does. Frankly I don't care. The starter has an incredible amount of torque due to reduction, and I doubt the compressor strains it at all.

[SS-Traveller]

Originally Posted by Atlblkz06

* If your turn off your car at a light, the compressor is off, but the blower is on.

Turn off your car and the blower also stops. Only ICE and cigarette lighter socket are powered up. Turn the key back to the 'on' position, and the blower, AC (auxiliary fan) and AC compressor clutch are all switched on. Leave the switch on for 15 minutes and you can have a flat battery.

Frankly I don't care. The starter has an incredible amount of torque due to reduction, and I doubt the compressor strains it at all.

You must be joking! This, from someone who doesn't jumpstart his car?

[star_aqua]

Guys, this thread must have been specific to a particular car. this discussion will be never ending because the HVAC control logic are not same for all the cars. say for example if you consider a FIAT palio, all the accessories which include blower unit, aux fan, AC clutch, head lights will be cut off during engine cranking. its done within the key and not by an ECU. where as if you consider scorpio, the accesories are not cut off, but the AC, aux fan is cutoff during cranking. here it is done by the ECU.
And all the discussion here holds good for a M800 which doesn't take care anything by itself. one must avoid cranking M800 with AC switch ON. because the load on the battery is high(blower, radiator fan, AC clutch and starter) and in addition to this the starter draws more current due to engine coupled with the AC compressor.

[quickdraw]

It would be funny, trying to crank a M800 with every damn thing turned on. Just turn the key and she will just die on you.

No one can force anyone to do anything, exactly the reason the airhostesses request you. And someone who can deny them something they asked must be so heartless :(

[Jaggu]

@star_aqua: are you sure M800 doesnt have a cut off in the switch while cranking, IIRC they have it built into the switch, same with all maruti vehicles???

[star_aqua]

Originally Posted by Jaggu

@star_aqua: are you sure M800 doesnt have a cut off in the switch while cranking, IIRC they have it built into the switch, same with all maruti vehicles???

I am not sure about the MPFI M800 jaggu, but what i said is true for the carb M800. but in most of the MPFI engines, the AC compressor is controlled by the ECU.

[ghpk]

My town doesn't have even one Traffic Lights working, How do i save Fuel huh,
Yeah but i do turn the Ignition OFF, cause it saves fuel in best interest of ALL.

Still the traffic is Whistle Driven at-least in one town where i stay, Allahabad.
However recently read in newspaper, Govt. has approved very expensive traffic light system again to get Banged by Drunk Truck Drivers, Lol

[dustom_99]

well,,AC does not make any difference to starting of the car,nor does it drain extra current,thus it does not overload the battery..AC in car almost has nigligible current consumption(xcept blower which is hardly 45w+ some solinoid valves+some electronic gagetry if equiped with temp control AC)as the main enegry consumption comes from compressor only, which is directly belt driven from engine..and it starts cooling only when R134a gets under pressure of about 12mpa(usually may range upto 15mpa aswell).other parts like evaporator,condenser,ref bottle(reservoir)..etc either does not require power atall or just run on few watts. so i dont think it should be a dramatic as shortning the life of battery or self starter or sumthing else..and please!!! a battery is a battery because it can store power for future use!!whats wrong if some energy is drained in running your music or blower ,its now going to shorten anything,battery is doing just what it is suppose to do! if all hell broke loose and worst comes in sight..u just might end up with a drained battery...and might have to tow/push start..thats all..yes i agree u shud switch off ur headlights for sure whenever ur engine is not running..they are usually 65/95 watt power each side..and might drain ur battery pretty quickly..even this quickly i mean 20-40 mins if the battery is in gud condition..

[MBG_Evo]

Originally Posted by Atlblkz06

You guys are so high strung about the small stuff, you're going to die of hypertension before anything happens to your cars...lol

Good One!

Originally Posted by SirAlec

hold you horses people. lot of confusion here.

ac compressor comprises of following:
1. pulley, that revolves along with engine through Belt.
2. compressor pistons
3. magnetic clutch which engages the above two.

Guys! Simple enuf, break it down like SirAlec. But before we go ahead, i cant believe that NOBODY talked about this - Turning off your car on traffic lights so SAVE FUEL??

Ive seen a few adverts about this on indian channels lately! Impossible to save fuel by switching off your car at traffic lights. Imagine on a road with 5 traffic lights, you switch off the car for like lets say 3 mins approx. And right when you are about to crank it up, key to ignition, fuel pump kicks in, throws initial cranking fuel to your injectors, CRANK and your car starts. This is the same amount of fuel that you might have used in the 3 mins the car would be running, or less. Try this, crank your car, leave it running for a bit, switch it off and crank it up after 3 mins. Do this for like 5 times in 20 mins and you might see a puff of black smoke out of your exhaust. This is because of the simple reason that your engine is running rich (more fuel than oxygen) and this is because of the fuel pump pushing fuel to your engine everytime u turn the ignition on.

Back to the AC -

Compressor engages only when the engine is running. Reason? It uses the belts which are constantly moving to power its-self. Engines not running, no belts are running, no compressor action.

Try this. Start your car, and look at your engine bay. As your buddy to switch the ac on and you will see the magnetic clutch in action.

Next, is it safe to keep the ac running while we crank the car? Yes it is. BUT, not preferred/advised. This has already been answered to. You are simply overloading the complete process. Some cars cut off ac, some dont. Also, most cars cut off ac compressor under WOT/Full throttle. Why? Load

Tip: At driving speeds of more than 80 kmph. Do not turn the a/c on. decrease speeds to less than 80 kmph and ur safe with the ac compressor.

All what has been said will just add more life to the parts involved. Nothing done opposite will result in severe damage.

Hope this helps!

[IQBAL VEERJI]

Originally Posted by Jaggu

If you can switch off the compressor switch good, though no major harms since the modern day car circuit will cut off the ac compressor, blower etc before the engine fires up. They will be switched ON after a delay of 1-2 secs automatically after the engine is running.

Regular usage (like signals and short parking) i dont use the ac comp switch (leave it ON always) and just manage it with the blower switch , which will take care of the compressor also in Maruti vehicles. Only in the morning and cold starts, i run with blower ON for the engine to warm up a bit and then switch the compressor separately.

Technically no harm but being a car lover, definitely recommended to wait for few secs for engine to catch its breath

HI Jaggu but in my Maruti Van's Super King AC I have a single rotory control for blower and compressor to set the variable desired temp and to cut OFF the comressor I will have to rotate the knob till compressor gets cut OFF and disturbing the temp set after spending lot of time adjusting prefered temp,so I just rotate blower switch above compressor controller knob to OFF position, and turn the blower switch ON again when required without disturbing set temp. This practice is followed also when climbing steep gradients viz. bridges,ghats,steep climbs without labouring the engine.In fact I will prefer to remove the temp knob. I keep the AC switch OFF when starting the van,and switch OFF the AC 20 seconds before switching OFF the engine. My method of use is right or wrong please give comments?

[filcord]

Sorry if I have posted in the wrong thread. My question concerns re-starting the car a/c. I usually put off the a/c when climbing a hill. Then when coming down or on level ground , re-start the a/c. Is it advisable to wait for two-three minutes before re-starting, like one does with a home a/c?

The reason one waits to re-start a home a/c or refrigerator is because of high head pressure in the refrigerant system.
Does this apply also to cars?

[Samir Taheer]

I have to agree with MGB Evo. I've read in numerous places that switching your car off, for a few mins, is not really giving you any petrol savings. The car uses more petrol, whislt starting up, then it would during idle. Obviously, there is a time limit.

As for the swtich off, my old 800 (1985-86ish), if the ac is left on and you start the car, it takes a few seconds for the compressor to kick in. So it doesnt seem like its putting any load on the batter or engine.

@Filcord - why do you turn the a/c off when going uphill? So save fuel? I dont think it should make any difference if you turn it back on immediately.

[amit_mechengg]

in my alto whenever i hit the starter all the electrical load is cut of for around 2 seconds till the engine fires and then the AC , headunit etc start up.
and i think 100% of new modern cars use the same technology.

[honeybee]

Originally Posted by Perakath

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.

Even if the use of cellphones may not always interfere with the electronics of an airplane, I wouldn't wanna be trying that at 30000 feet.

Even if you keep the blower/fan on with the engine switched off, it will drain the battery. You will be caught with your pants down, so to speak, when the light turns green.

If you just cannot do without the AC, let the engine run. This way you will at least save the embarassment of having to get your vehicle pushed to a side, inviting curses from all the motorists around you.

Usually accessories such as the stereo or parking lights do not use much current. If you have LED lights, so much the lesser. However the blower or the headlights will typically consume more current. Specially if you have changed the headlight bulbs to a higher rating and are using a relay to power them, make sure you switch them off if the engine is shut.

Personally I keep the stereo on and if it's night, then the parking lights, whenever I switch off the engine at a red light. I have seen some cars parked on the street with their headlights on. You may be able to get away with it if you only halt for a brief period (a couple of minutes).

I once drove a battered M800 where you had to switch off every damn thing that used the battery before the battery could crank the engine.


Always remember: Being caught with a dead battery in the middle of the road is the worst thing you can cause. As a responsible driver, you must ensure your vehicle is always ready to move. Running the blower/AC with the engine off and losing your battery only means the occupants have to sweat it out pushing you to the side and wait for a backup.