I've always wondered, should you shut your AC off first before shutting your car off? I always do whenever I drive someone's car (my AC doesn't work) but I never see anyone else do it. Am I just being nitpicky?
Before power management systems I would turn off before shutdown and even a block or 2 before to prevent odors. Newer vehicles its probably not an issue
I am in the habit of doing it, too. But, it's because my dad told me that if I didn't I would be forcing the starter to turn the A/C compressor when I restarted the engine. This was on a 1972 Pontiac so who knows, it may have been true. I don't think it really matters anymore, but old habits like this are really hard to kick.
I normally turn everything off before shutdown, I want a clean start with minimal electrical load and where I can hear the motor and mechanicals before getting underway (to listen for any unusual sounds/noises). A/C would be no different.
I figure turning the AC off a few minutes before stopping the car gives the water droplets in the engine bay a chance to evaporate quickly. In any case, I don't want the AC running as soon as I start the car next time. For one, depending on your starting rpm in fast idle (1500-2000 rpm+) your AC compressor spins right up from 0 to higher rpm. The only thing worse is turning it on when at highway speeds (2500+ rpm). Surely this is not ideal for compressor longevity. I'd much rather turn on my AC when the car is at low idle (800-1100 rpm). It will then ramp up with engine speed.
I never gave it much thought. In 40+ years of driving I typically turn AC of heat off just before I shut the engine. I've never had any AC problems, other than Ford's leaking "O" rings, and a pin hole in 20+ year old AC hose.
I will always shut the A/C off before shutting the car down, but usually only a few seconds before.
Don't know why...I leave the heat on when it's cold, never even really thought about shutting that off before shutting the car down unless I expect it to be MUCH warmer the next time I turn the car on.
Originally Posted By: 69GTX
I figure turning the AC off a few minutes before stopping the car gives the water droplets in the engine bay a chance to evaporate quickly. In any case, I don't want the AC running as soon as I start the car next time. For one, depending on your starting rpm in fast idle (1500-2000 rpm+) your AC compressor spins right up from 0 to higher rpm. The only thing worse is turning it on when at highway speeds (2500+ rpm). Surely this is not ideal for compressor longevity. I'd much rather turn on my AC when the car is at low idle (800-1100 rpm). It will then ramp up with engine speed.
the compressor is constantly cycling on and off. even @ highway speeds.
In my car the AC is always on, even during winter. The climate control uses it for moisture control. Not much point in fiddling with the buttons -- set the temperature and the car decides the level of AC and/or heat. The car has a huge battery in the trunk so that's not an issue.
I don't think it makes a difference as far as electrical load is concerned. A lot of cars will shot off different systems during cranking, like radio, lights etc.
I do, however, turn off the AC, but leave the fan running, few minutes before arrival to prevent bad smells in manually operated systems.
With auto climate control, I leave the system in auto mode pretty much 100% of the time.
Originally Posted By: ARCOgraphite
You should shut the A/C down a few Miles/Minutes before you plan to shut off the car but leave the interior fan running.
I was always curious about this, my dad always tell me to take if off before i shut off and if i take off the ac not to put it on right away as the compressor needs to equalize
Originally Posted By: mightymousetech
I always turn off my A/C several minutes before shutting the car off. I hate the smell when the evap is left damp and bacteria grows in there.