Ok, I had the climate control blower replaced on my 88 300e. The day after, I left it idling and the abs light came on(system voltage below 10 volts.) Car has had new alternator, blower motor, belt tension,

When cold, systems are fine, a/c, lights, on sitting still, charging properly.

As car warms up, starts drawing way more amps than system is producing and discharges battery. The work is being done by a shop in Austin TX with excellent history.

2 blower motors and 2 alternators have been tried. HELP!!!
What the heck would make a car do this?

OK I'll bite... how many amps does it draw?

The inside fan can use up to 20 amps and so can the aux fan in front of the radiator. If you have an early car you should update the wiring and alternator to the 80 amp version used after 1990.

The problem we see with many early cars is that the 65amp alt (even the 70 amp ones with spade connections at the output) only produce 50-60% output at idle. The bigger alternators not only put out more but they put out 75% or more at idle.

Basically its all a matter of addition. 20a (inside fan) + 20a (outside fan) + 10a (headlights) + 15a (ignition/fuel pump)= 65a. The alternator is lucky to do that at 2000rpm. Its probably more like 35a at idle. It all adds up to big trouble.



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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

like negitave 25-30 amps when warm and at idle. any idea why it is fine when cool?
I am gonna call MB dealer and see if they will take back 70 amp unit.

I have also seen corroded wires cause this. The wires at the alternator will corrode or break. It is not easy to see though. Your alternator is not charging at all at idle. I have done the mod mentioned by Steve, but most of the time it will be negative 2 amps, not negative 25. Check the blue wire at the alternator.

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Benzmac:
Donnie Drummonds
300E
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Engines usually are in fast idle mode when they are cold. The fast idle produces more current. That may be the reason why the system is charging during cold start. Speed up the engine rpm to the same rpm as it is cold to see if my suggestion is correct.

David

Will the 80 amp unit bolt right up?
Wiring advice on changing over?

I hate to treat the symptom, but may have to, just to get back on the road.

Thanks for the help guys

Alternators are less efficient when hot. That's why they have the cooling duct. Or so I was told by a reliable source, and have observed on my Porsche which did the same thing as the alternator got weak.

Chuck

It will bolt up, but not wire up. The harness has to have 3 rings soldered on.

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Benzmac:
Donnie Drummonds
300E
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM