Does A/C create a heavy load on the alternator/battery? - PeachParts Mercedes-Benz Forum

Blevinsax · #1 06-04-2007, 01:55 AM

Does A/C create a heavy load on the alternator/battery? Just curious because I have noticed that when starting the car in the morning, it sounds like the battery is going dead, but only after driving all day the previous day with A/C. If I drive without A/C, the car seems to start easier the next morning. Maybe the A/C is pulling too much power from the alternator away from recharging the battery?

I will not be surprised if the battery is just dying - it is commonly understood in Las Vegas that your car battery will only last one year after moving here. The heat just destroys them! The exact same thing has happened to every car we have owned here - Almost exactly one year and the battery goes kaput! Maybe that's what I am experiencing with the Benz since I've had it in Las Vegas about a year now.

Thanks for your input/experience/advice.

300SD81 · #2 06-04-2007, 02:16 AM

Are you trying to start with the AC on? If the compressor clutch is engaged, there is an extra drag on the engine the starter has to turn.

#3 06-04-2007, 02:56 AM

The A/C clutch only takes a few amps. The blower takes much more.

babymog · #4 06-04-2007, 03:15 PM

Yes.

The blower takes moderate current, and the aux fan(s) in front of the radiator take more still. All combined you can discharge the battery with the engine at idle, especially with lights on etc.

I just jump-started a Lexus last week left idling too long with all accessories running on high.

Blevinsax · #5 06-04-2007, 07:55 PM

Thanks for the great info, but I think I just found out why my car has been having trouble starting in the morning...

I just found out from (and walked home from) my mechanic that my alternator is going bad, so I am having it replaced. I have several additional electric accessories installed (VegTherm Mega, Greasecar kit - doesn't use much, but some - and 3 stereo amplifiers. What can I say, I am a jazz musician, so I am an audiophile - I like to listen to jazz in the car and actually HEAR the bass solos!!) so I am considering having the stock alternator replaced with the gasser model with a higher (85 amp) output instead of the lower (60 amp) output of the standard model for the car. Is that a wise decision or should I reconsider? Am I completely out to lunch on this???

Thanks for all the help here - you guys are seriosuly helping save my butt on these (diesel) cars!

Brian Carlton · #6 06-04-2007, 08:14 PM

Quote:

Originally Posted by Blevinsax

Is that a wise decision or should I reconsider? Am I completely out to lunch on this???

That is a wise decision.

Blevinsax · #7 06-04-2007, 08:35 PM

Quote:

Originally Posted by Brian Carlton

That is a wise decision.

Thanks Brian - now I feel better! (Except for the fact that I know this will be an expensive repair!)

Do I have the amp numbers correct? The diesel alternator is 60 amps and the gas alternator is 85 amps?

babymog · #8 06-04-2007, 09:40 PM

I would go higher than that if upgrading anyway. For example, a Jetta from the mid '80s was a 90amp, ... Mercedes for some reason installed sadly undersized charging systems in the '80s and early '90s.

You'll want to upsize the power lead from the alternator also.

vstech · #9 06-04-2007, 10:06 PM

search for saab on here. you will find a lot of info about converting to a 115 or larger amp alternator.
John