Air-Cond On When Starting

[absidian]

@meetoo: I can relate to the process control engineer part of you since i am also from a control background and do the sequential on/off regularly too. This thread is really amusing for me because ironically I find myself questioning my own actions when I know there is in fact a cut-off but hey what's important is, like you say, reducing unnecessary stress and unscheduled maintenance events to prolong its life expectancy.

 

[meetoo]

before i crank the engine, i will turn the key to an on position, wait a few seconds then crank. but during the waiting period, the radio will on. and when i crank, the radio doesn't cut off. its still playing.

i haven't tried with the aircon on before starting. i'll try tomoro. hmm....funny.

Same with me! When my wife leave things on and I start the car later, I notice that things don't cut-off completely. Headlight will just dim and flicker, the radio will go soft but still on, etc. This suggest more of brownout than cut-off to me. That's why if LCP has seen the cut-off in the circuit diagram, I'd like to know exactly where it is and in what form.

Very strange...some cars got cut-off, some don't, some respond to handclap...

 

[SuperCharger]

i think it would be better starting the car with all the electronics off for eg air-cond, radio & lights.. basically when the ignition is on and before you crank the starter, these electronics will be powered on directly by the battery.. so in a way the battery life span becomes shorter in the long run..

it's not hard switching off the air cond, radio, lights & etc as it reachable by the driver with just a click...

that'z my 2 1/2 cents..

 

[meetoo]

Guys, I tried an experiment this morning before leaving for work. With key in 2nd position, I switch on headlights, wipers, radio and aircond. Then crank the engine. Result:

Headlights - flicker but stay on
Wipers - carry on working, not even slow down
Radio - stop for 1 sec
Aircond fan - carry on working, not even slow down

So LCP, absidian, why my 2003 E46 has no cut-off that you mention? Maybe the rest of you can try on your car and report results.

Oh...also try a hand clap but no effect on anything, except my wife gave me a funny look

 

[SuperCharger]

I think your battery is healthy... so when u crank the engine, the starter doesn't drain much power from the battery and your electronics continue to work.. so not really a cut off thingy but it depends on the condition of your battery..

 

[meetoo]

Agreed Supercharger, but that not the issue. The issue is whether there is a cut-off or not. Whether the magnetic clutch of the aircond compressor will be engage or not when you crank the engine, putting extra load on your starter and battery. That's what this thread is debating.

 

[David Yong]

Oh...also try a hand clap but no effect on anything, except my wife gave me a funny look

Ai yoh.... try doing it again today and make sure u clap harder

 

[okow]

I believe it to be your on-board computer that recognises your driving habits and characteristics. If you keep switching off your air-con everytime before you shut down your engine, that will be recognised as a 'user habit' in time to come. Try it.

 

[meetoo]

I don't think so, okow. That applies to your throttle and brake usage, and only available in certain model. It doesn't apply to accessories like aircond, lights, wiper, radio even in those models.

 

[LCP]

Okay okay, very sorry guys, looked up both my Haynes and Bentley service manuals for E36, there is no cut-off at the crank position for many items... I must have been looking at too many circuit diagrams of cars already, I have got this, errr, "fetish" for schematics diagrams since I was a kid, can't take my eyes off them the moment I see one.

Here's what happens in my car... on the aircon compressor, no way to turn it on if the engine is not running, only the blower and aux fans will run if the ignition switch is turned on, and the compressor will only come on a few seconds after the engine has been started, if the aircon is left on when starting. My radio cuts off fully when the ignition switch goes into crank mode, and will reboot again after finish cranking...

As for my headlights (excluding position lamps), can't turn it on (in "off" or "acc" modes) unless the switch is in "run" mode, not sure whether it cuts off when in cranking mode.

 

[meetoo]

Thanks LCP. Very useful information! My practical (on E46) shows that the headlights can be on in position 2 and will flicker (brownout) when the engine is cranked.

Interesting that the AC compressor will only engage a few seconds after the engine has started. Does the manuals show how that is achieved? I still have a feeling that the magnetic clutch will be engaged when the electricals are switch on in position 2, thus presenting an extra drag for the starter and battery.

 

[acidburn]

Yo guys..
I already checked with BM engineer and he said that engine CPU will cut off any single electric signal during crank the car up. But it is advisable to turn the aircond or radio off to prevent the sudden electric signal which can leads to shortern down the electrical gadget lifetime. Nevertheless it still have fuse to split this sudden signal though.

 

[spikyone]

I always switch off the a/c in my 328 at d last position b4 starting, so that when i start the car it starts without a/c running. Cos if i dont, the a/c will cut in straightaway..I dont think thats good, especially when cold start. THink of it this way: U just got woken up by alarm clock then straightaway got forced to run sprint race (sudden load@ cold start due to a/c compressor cut in)..feel good o not? at least give time to warm up 1st mah..

 

[alxy]

Mine stays off when i switch it off previously. Same as my friend's. I have a 2001 E46 325 and he has a 2004 E46 330.