Charging/Electrical Problems With A/C On? - PeachParts Mercedes-Benz Forum

gmercoleza · #1 08-31-2006, 09:51 AM

97 E320 W210, 155K miles. Brand new battery, alternator was new Bosch replaced about 1 year ago. Battery & alternator tested fine a couple weeks ago.

As soon as A/C is switched on, the dash, dome, and headlights flicker as if the voltage regulator or alternator is shot. If driven long enough, the battery will drain completely as indicated by failure to crank and start after it is shut off.

If vehicle is driven without A/C engaged, none of these problems is experienced and the car starts fine each time without any problems.

Any ideas?

david s poole · #2 09-01-2006, 12:36 PM

now you need to start checking grounds.check both ends of ground cable at battery.check main ground from bell housing to chassis.now check under hood for ground points to chassis and make sure clean.operating ac with high blower is drawing 35amps all by itself.did you check alternator output with clampon ammeter after installation?can you run a ohm check between alt body and ground on battery[use very low scale typ 200 ohm [not kohm or megohm]you may need to ground the alt body to the chassis.just a few thoughts to keep idle hands busy.

porkface · #3 09-01-2006, 01:07 PM

unplug the cooling fan and try again. i went round and round with a 210 that refused to act right until i replaced the fan assy. even went so far as to put the old alt on after i'd replaced the fan assy to make sure it was dead. the old fan ran alot of hash into the circuit and it looked like ac voltage bleeding out of the alt. just my 2 cents. good luck, chuck.

gmercoleza · #4 10-02-2006, 02:23 PM

Just talked to my buddy (owner). A month ago when I first reported this issue, I also told him to keep driving the car but without the A/C. He has been doing this and hasn't run into any issues. Hasn't had to jump the car, and the flickering in the dash and headlights is all but gone. Definitely sounds like an undercharging condition to me, as if the system can't overcome the electrical load that the A/C puts on the system.

He is going to leave the car with me in a couple weeks when he goes on vacation. I will start by looking at the battery cables (pos & neg), the grounding strap(s), and the harness going to the alternator. Interestingly, he left the car at the dealer (Ewing in Plano) and paid them $200 for a diagnostic. They did not find any charging issues but told him his gauge cluster was bad along with a few other things such as the rearview mirror needing replacement. They did not elaborate on the cluster. The cluster has been "bad" for 4 years but he never had it replaced. He never had these electrical issues until the last 6 months or so - is there ANY way possible that the cluster could be causing this? Seems to me that if the cluster was the problem then it would occur both with the A/C on and off.

I appreciate the suggestions given previously - any others?

david s poole · #5 10-02-2006, 03:04 PM

the only way the cluster could cause this is if the a/c was turned on before starting the car and somehow the battery light failed to illuminate[before turning to start position].then the alternator would not be getting exciter current and would not charge.this is unlikely but easy to check.much more probable that a/c straining the friendship with the grounds on the car.

gmercoleza · #6 10-02-2006, 03:21 PM

Thanks David, I think you are right. Any pointers on readings and measurements, for instance what I can look for with the VOM hooked up to the battery while idling? Also, what type of resistance am I looking for between the alternator body and the negative battery post? Given the great distance, can I use a piece of Romex to assist in accomplishing this measurement?

david s poole · #7 10-02-2006, 04:29 PM

first check the ground from alternator body to good ground post under hood[body ground].there should be no impedance[ohms] measurable on 200 ohm scale.check very carefully the main ground from bell housing to body.check at battery for good ground between negative post and body.p.s. be sure to have key off when doing any of this.

porkface · #8 10-02-2006, 06:09 PM

you find the answer, please let us know. this 1 sounds a little different than the 1 i had. thanks, chuck.