I’m curious whether modern automobile electrical systems are designed to suspend accessory operation during starting. My new ride actually runs the starting sequence itself (I don’t “hold” the starter, it handles that). It seems that it would have enough logic to keep the A/C clutch disengaged and electronics offline until the alternator’s producing current.
I ask this because my new truck actually came with a remote start feature on the keyfob. I’ve only tried it once, but pushing the start button causes some clicking and whirring under the hood, and after a few seconds of contemplation, the engine starts itself. I wonder whether one could leave the A/C set to a desired temp, and pre-cool the interior a bit before entering?
I know some of our members have a lot of mechanical expertise, hopefully they’ll weigh in and fight my ignorance on this.
I don’t have remote starting (not legal here) but if I leave the climate control on ‘auto’ and start the car, it will not actually start blowing air until the engine is warm enough to make it work. Once the engine is warm, it starts to blow hot or cold air.
I don’t have a remote starting vehicle and I don’t have any experience with these types of vehicles, but I’d be inclined to say that you do not have to turn off the accessories and AC. I base this solely on the idea that nobody would want a vehicle with remote-start if you have to turn everything OFF each time you get out if you intend to use the remote-start feature later. That would be a terrible selling point and a major design flaw.
My 1974 Beetle doesn’t turn anything off when starting, although to be fair, the only accessory in the Bug is the radio.
Pretty much anything newer or more complex keeps power off to the accessories when starting. Even my simple 30 year old beater pickup truck turns off all of the accessories while starting.
You can certainly leave the AC on and cool the car with remote start on a modern car. Anything new enough to have a remote start wouldn’t have any issues with it. Heck, you could probably hack a remote start into any car back to at least the 1970s era vehicles and they wouldn’t have a problem with it either. Even those older vehicles only powered the accessories when the key was either in the run position or turned all the way back to the accessory position. When the key was in the start or off position most of the accessories weren’t powered.
I believe there is a relay connected to the starter. When the voltage goes high on the starter motor, it cuts off power to all but the ignition system.
More modern cars likely do it electronically, but back in the day I know there was a relay that controlled all of that activity.
I don’t know, but my wife always freaks out when she sees me leave the heater/AC on before starting the car. She swears you have to turn it all off first or you’ll ruin it. Her dad was a mechanic, so she knows what she’s talking about. But I’ve been doing it all my life and never had a problem. Luckily we have separate cars.
yes. most cars control the starter via the PCM or BCM. all the ignition switch/start button does is tell the BCM that you want the engine to start. when you turn the key/push the button, the BCM sets the power status to “START” and orders all non essential modules to go into standby. then the PCM activates the starter solenoid and cranks the engine until it senses it has reached self-sustaining speed, then disengages the solenoid. the power status is changed to “RUN” and the rest of the modules then wake up and do their thing.
edit: the old way was that the ignition switch was a mechanical switch which directly controlled a number of circuits, and was designed to physically cut power to any accessory which shouldn’t be operating while the starter was engaged.
My mother’s 1962 Chrysler blew a fuse when you tried to start it with the AC turned on, leading to much colorful language from my father when he had to run up to Western Auto to get a new box of fuses every time there was a heat wave. I’m sure today’s cars don’t have that problem, but that’s how stories like this get started.
When I was a kid I was told that you had to turn everything off, either because it could run down the battery or because there might be enough power to start the car. However when I forgot to do this nothing bad ever happened. I never saw any reasonable evidence supporting this legend.
Blowing fuses would seem to indicate a fault in the electrical system, not a feature. But a lot of early '60s cars were crap anyway.
When the weather is extremely hot or cold I’ll turn the heat/AC to max when I park it so that I can remote start the next time and have it comfortable when I go out to leave. Remote starting doesn’t turn on the radio or any accessory outlets until I get in and press the start button.
Thanks everybody for your replies. Since the climate control is automatic, I suppose I’ll just leave it set to a comfortable temp and not mess with it when I stop/start the vehicle.
This is perplexing to me. Where are you and why would such a feature be illegal? The car manufacturers seem to have taken suitable precautions to ensure against theft or accidental movement. At least on mine, it will only run a short time before shutting itself back off.
Yeah, my Wife’s 2016 Subaru Outback locks the doors if you auto start it. And, once you get in, you have to push the start again. So if a door opens after the auto start (say someone broke a window and opened a door) it has to be restarted. And that will only happen if the key fob thingy is within range.
I suppose someone could break a window, crawl in without opening a door and defeat that.
a. During startup, there are large voltage swings on the car’s main power bus. This can mess up electronic accessories - this is why the HMD usually blanks itself during starting, etc.
b. You can pre-start a car to run the A/C, it’s going to do the same thing that turning the key does, the way those remote start kits are wired.
c. Hybrids and EVs do a much better job of this. You can remotely turn on the air conditioning in a hybrid or EV, and the A/C compressor just starts up, cooling (or even heating the car for the new Prius Prime with a heat pump).
The engine just runs intermittently, and/or in an EV, just a little bit of the massive battery pack gets drained for every hour the A/C runs.
A slight drift but ---- what about standards/manual transmissions? My Subaru, for example, requires you to depress the clutch before it will engage the starter. Do those kits have a bypass for that action? Do factory set-ups differ in some way? I’m curious now that I think about it.
