Turning Engine on with Airconditioning On
Thread Starter
Super Member
Joined: Sep 2007
Posts: 978
Likes: 3
From: Essex County, NJ
2011 E350 Sport 4Matic - P2 & Drivers Assist / 2010 C300 Sport 4Matic - P2 / 2013 Porsche Cayenne S
Turning Engine on with Airconditioning On
Is it damaging to the engine to have the AC already in the on position when turning it on ? My father told me (about 10 years ago) that it puts extra strain on the engine upon startup to have the AC in the on position. I was always taught to turn the engine on and then turn the AC on. I've been doing it ever since and was wondering is anyone else doing it ?
MBWorld Fanatic!
Joined: Mar 2004
Posts: 5,017
Likes: 16
From: Ft. Lauderdale Area, USA
2015 ML 350
The accessories only work when the ignition is in the "on" mode, they temporarily lose power as the car enters crank mode.
On a conventional car you can demonstrate this by turning on the A/C full speed, turning off the car & then very slowly turning the ignition key. When the key goes from off to on the A/C will blow, and the radio will play. As you continue to turn the key slowly past "ON" to "start", all the accessories will first turn off and then the starter will be engaged. As soon as the key is released and falls back into the "run" position the starter will stop cranking & all power will again be sent to all accessories.
Engineers want the full power of the battery to crank a cold engine.
He is wrong.
On a conventional car you can demonstrate this by turning on the A/C full speed, turning off the car & then very slowly turning the ignition key. When the key goes from off to on the A/C will blow, and the radio will play. As you continue to turn the key slowly past "ON" to "start", all the accessories will first turn off and then the starter will be engaged. As soon as the key is released and falls back into the "run" position the starter will stop cranking & all power will again be sent to all accessories.
Engineers want the full power of the battery to crank a cold engine.
He is wrong.
MBWorld Fanatic!
Joined: Dec 2006
Posts: 6,499
Likes: 335
From: Europe
223.168 & 213.012 & 906.633 & 214.005
I guess his father wasn't completely wrong, just that modern cars do the same thing automatically that he did manually for older cars.
The demonstration by Barry does not show if the AC compressor actually is disengaged but I believe it is. The new compressors actually run (rotate) always but they still can be "turned off".
The demonstration by Barry does not show if the AC compressor actually is disengaged but I believe it is. The new compressors actually run (rotate) always but they still can be "turned off".
Thread Starter
Super Member
Joined: Sep 2007
Posts: 978
Likes: 3
From: Essex County, NJ
2011 E350 Sport 4Matic - P2 & Drivers Assist / 2010 C300 Sport 4Matic - P2 / 2013 Porsche Cayenne S
The accessories only work when the ignition is in the "on" mode, they temporarily lose power as the car enters crank mode.
On a conventional car you can demonstrate this by turning on the A/C full speed, turning off the car & then very slowly turning the ignition key. When the key goes from off to on the A/C will blow, and the radio will play. As you continue to turn the key slowly past "ON" to "start", all the accessories will first turn off and then the starter will be engaged. As soon as the key is released and falls back into the "run" position the starter will stop cranking & all power will again be sent to all accessories.
Engineers want the full power of the battery to crank a cold engine.
He is wrong.
On a conventional car you can demonstrate this by turning on the A/C full speed, turning off the car & then very slowly turning the ignition key. When the key goes from off to on the A/C will blow, and the radio will play. As you continue to turn the key slowly past "ON" to "start", all the accessories will first turn off and then the starter will be engaged. As soon as the key is released and falls back into the "run" position the starter will stop cranking & all power will again be sent to all accessories.
Engineers want the full power of the battery to crank a cold engine.
He is wrong.
MBWorld Fanatic!
Joined: Nov 2004
Posts: 1,691
Likes: 143
W221 S600, W220 S55 AMG Kompressor, W124 300E, W140 S320, W210 E3204M W164 ML320 Bluetec
Is it damaging to the engine to have the AC already in the on position when turning it on ? My father told me (about 10 years ago) that it puts extra strain on the engine upon startup to have the AC in the on position. I was always taught to turn the engine on and then turn the AC on. I've been doing it ever since and was wondering is anyone else doing it ?
Senior Member
Joined: Sep 2007
Posts: 332
Likes: 0
From: Long Island, NY
2004 E500 Wagon 4Matic
I had a flat battery a week after I got my car last year. I won't go into why (too embarassing) but ever since then I turn off my A/C and COMAND before I switch off the engine. More habit than anything, but I am comfortable with it.
Thread Starter
Super Member
Joined: Sep 2007
Posts: 978
Likes: 3
From: Essex County, NJ
2011 E350 Sport 4Matic - P2 & Drivers Assist / 2010 C300 Sport 4Matic - P2 / 2013 Porsche Cayenne S
Trending Topics
MBWorld Fanatic!
Joined: Nov 2004
Posts: 1,691
Likes: 143
W221 S600, W220 S55 AMG Kompressor, W124 300E, W140 S320, W210 E3204M W164 ML320 Bluetec
MB World Stories
The Best of Mercedes & AMG
6 Mercedes Models That Did NOT Age Well (But Are Somehow Still Cool)
Verdad Gallardo
Manual Mercedes? 6 Times Sindelfingen Let Drivers Have All The Fun
Verdad Gallardo
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Verdad Gallardo
8 Classic Boxy Mercedes Designs That Have Aged Like Fine Wine
Verdad Gallardo
Flawlessly Restored Mercedes 190E Evo II Heads to Auction
Verdad Gallardo
Electric Mercedes C-Class Unveiled: 11 Things You Need to Know
Verdad Gallardo
Mercedes EQS Gets A Major Update: Everything You Need to Know
Verdad Gallardo
5 Underrated Mercedes-Benz Models That Don't Get the Love They Deserve
Verdad Gallardo
Mercedes 300D Has Pushed Well Past 1 Million Miles and It Ain't Stopping
Verdad Gallardo
Senior Member
Joined: Sep 2007
Posts: 332
Likes: 0
From: Long Island, NY
2004 E500 Wagon 4Matic
Oh, alright...
I left the glove box open. Teeny tiny little bulb in there drained my battery from Thursday night to Saturday morning. My MP3 player had a little six inch audio cable to go into the Aux. So, when I was driving I would leave the glove box open so I could reach the unit. That night I didn't close it.
Y'all happy now?
I left the glove box open. Teeny tiny little bulb in there drained my battery from Thursday night to Saturday morning. My MP3 player had a little six inch audio cable to go into the Aux. So, when I was driving I would leave the glove box open so I could reach the unit. That night I didn't close it.
Y'all happy now?
Thread Starter
Super Member
Joined: Sep 2007
Posts: 978
Likes: 3
From: Essex County, NJ
2011 E350 Sport 4Matic - P2 & Drivers Assist / 2010 C300 Sport 4Matic - P2 / 2013 Porsche Cayenne S
Oh, alright...
I left the glove box open. Teeny tiny little bulb in there drained my battery from Thursday night to Saturday morning. My MP3 player had a little six inch audio cable to go into the Aux. So, when I was driving I would leave the glove box open so I could reach the unit. That night I didn't close it.
Y'all happy now?
I left the glove box open. Teeny tiny little bulb in there drained my battery from Thursday night to Saturday morning. My MP3 player had a little six inch audio cable to go into the Aux. So, when I was driving I would leave the glove box open so I could reach the unit. That night I didn't close it.
Y'all happy now?
Senior Member
Joined: Sep 2007
Posts: 332
Likes: 0
From: Long Island, NY
2004 E500 Wagon 4Matic
Thing was my wife was pi$$ed that I got an MB at all, especially with 88k miles on it. I said "Don't worry, it's a MB. Will run for years". And then it craps out on me.
I was just waiting on the smug smirk, but thankfully I was busy with the battery charger
