[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.

So when you press the ac button on, the magnetic clutch is activated through battery/alternator and pulley drives the pistons. (if blower fan should be on too)

So when you crank the engine with ac in on position the starter motor has to do double the work as the magnetic clutch is engaged and it drives the compressor pistons.

I normal case (when ac is off) it would only revolve the pulley while cranking.

[d3mon]

AFAIK, the AC compressor is disconnected while cranking the engine, along with some accessories like the stereo system (which can be noticed easily)

So no difference, apart from the really old cars like 800, which did not have this feature.

[rapidsnail]

Originally Posted by d3mon

AFAIK, the AC compressor is disconnected while cranking the engine, along with some accessories like the stereo system (which can be noticed easily)

So no difference, apart from the really old cars like 800, which did not have this feature.

I second that, My UVA disconnects AC, Headlamps and ICE when cranking. The AC then switches on 2-3 sec after starting the car.

My 800 doesnt even bother to switch off the radiator fan when car is switched off (in ignition mode) and AC switch is on.

So basically all new company fitted AC cars can be switched on while AC is turned on. I however also recommened to turn on the AC only once the car has warmed up, preferably after cold start.

[SS-Traveller]

Originally Posted by d3mon

the AC compressor is disconnected while cranking the engine

Originally Posted by rapidsnail

I second that, My UVA disconnects AC, Headlamps and ICE when cranking.

Not all cars, even modern cars, cut power to the auxiliary fan and AC clutch when cranking the starter. If your car does that, good, you can continue to keep AC and blower switches on while cranking. If it doesn't, well, switch off before cranking.

[Perakath]

Originally Posted by SirAlec

So when you crank the engine with ac in on position the starter motor has to do double the work as the magnetic clutch is engaged and it drives the compressor pistons.

I normal case (when ac is off) it would only revolve the pulley while cranking.

What's wrong with the motor doing double the work? It's not a human being, to get annoyed or something The fact that cars start with the a/c on show that the starter motor is capable of it. And I've never heard of anyone's starter motor going bust...

Originally Posted by d3mon

AFAIK, the AC compressor is disconnected while cranking the engine, along with some accessories like the stereo system (which can be noticed easily)

When I restart my Zen at traffic lights, sometimes the stereo cuts out and sometimes it keeps playing. I assume it has something to do with battery charge levels. Of course, I'm happy when it doesn't cut out, because otherwise the song that was playing starts from the beginning, after a read-CD delay of a few songs!

[ImmortalZ]

Starter motors do go bust. When they do, your wallet goes bust.

In my Civic, when I crank, the stereo and A/C are turned off temporarily. I can only imagine that the compressor clutch is also disengaged. The OEM stereo continues where it left off in any case, so I don't care. The headlights and other ancillary lighting stays on though - and I can see them dip when the motor cranks. So I do turn them off before starting the car.

[SS-Traveller]

Originally Posted by ImmortalZ

Starter motors do go bust. When they do, your wallet goes bust.

Well said!

In my Civic, when I crank, the stereo and A/C are turned off temporarily. I can only imagine that the compressor clutch is also disengaged. The OEM stereo continues where it left off in any case, so I don't care. The headlights and other ancillary lighting stays on though - and I can see them dip when the motor cranks.

The AC cabin blower is turned off temporarily, but check under the bonnet when asking another person to crank, to see whether the AC compressor clutch goes "tic" and the auxiliary fan turns off when cranking. If not, these are extra loads on the battery and starter.

[tazmaan]

If the compressor is kept on when the engine is started, the starter will have to move the engine along with the compressor putting extra load on the starter. This will effect the life of the starter along with the battery.

Avoid starting the car with AC on. For signals you can have the blower on with AC switched off. You will get cool air for some time. Turn off both blower and AC while starting the car.

[Spitfire]

Harm or not. What does it take to flip a switch off and then on?

[Trust_In_Thrust]

Originally Posted by Spitfire

Harm or not. What does it take to flip a switch off and then on?

I believe this something is known as convenience and manufacturer of vehicle ought to take this in mind while designing car electrical system.

[rajivanoj]

If AC should not be in 'ON' position while cranking engine, it will be irritating to switch AC off and shut engine at red signal, and again crank engine and switch on the AC after green signal.

I think this dont make sense, to save fuel by 20% as said by govt Ad,

May be, except AC cars at signals, others can save fuels.

[quickdraw]

Originally Posted by Perakath

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.)

Actually they do. But theres nothing the airlines can do. If they install signal jammers then it would jam their own communications as well. Moreover they cant just ask everyone to hand their cellphones and return them after the flight is over there are too many privacy concerns and other tensions involved. So they just politely ask.

[Perakath]

Privacy and tension would take a backseat if aircraft safety were truly compromised. They could have lockers, or take only the batteries-- something could be done. I believe the truth is that "interference with navigational systems" is a fear, nothing more. Imagine a time when there were no security screenings of luggage. Your 'privacy and other tensions' arguments could have been raised there too if it were suggested that every single person and piece of luggage be scanned before entering the 'plane!

Similarly, if starting with the a/c on were known to significantly reduce starter motor life, rather than place some notional "toll" on the "hardworking motor", the system would be engineered to make it impossible. The ignition would refuse to engage, or something. It's like how you can't shift into reverse gear when the car is moving forward at high speed.

Again-- I personally switch off a/c and headlights/parking lights before starting, every time!

[quickdraw]

Originally Posted by Perakath

Privacy and tension would take a backseat if aircraft safety were truly compromised. They could have lockers, or take only the batteries-- something could be done. I believe the truth is that "interference with navigational systems" is a fear, nothing more. Imagine a time when there were no security screenings of luggage. Your 'privacy and other tensions' arguments could have been raised there too if it were suggested that every single person and piece of luggage be scanned before entering the 'plane!

Similarly, if starting with the a/c on were known to significantly reduce starter motor life, rather than place some notional "toll" on the "hardworking motor", the system would be engineered to make it impossible. The ignition would refuse to engage, or something. It's like how you can't shift into reverse gear when the car is moving forward at high speed.

Again-- I personally switch off a/c and headlights/parking lights before starting, every time!

It has nothing to do with privacy and tensions, it interferes with the Radio and Navigation systems of the Aircraft. Ask any pilot present on T-BHP. Be considerate and switch them off/ to airplane mode. While on board.

The AC compressor doesn't switch on when the engine isnt running. But like you said its a good practice to switch off the lights and AC while cranking. It really strains the battery (the lights)

You can shift into reverse if you try really hard. Just dont let go of the clutch

[Perakath]

You're the one who brought up "privacy issues and other tensions"!

My point is that while it may be good practice, when it comes down to it it's not essential to turn off the lights, a/c, or cellphone while starting a car or an aeroplane