The 3a draw from the AC clutch coil is not going to be enough to make the alternator slip. On the other hand low voltage will cause the AC clutch to slip which is the likely source of the noise. Either way, the alternator is not doing its job either because of an internal failure or a bad connection.

Its time to pull the alternator or at the very least the brushes. Its all easily accesed through the bottom.

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CENSORED due to not family friendly words

Don't ask me how I know, but it IS possible to install the serpentine belt incorrectly, and then it will squeal whenever you engage the AC.

Check a diagram for the routing and compare to your engine.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

The ground wires are ok...no oil on the alternator. Vehicle has no oil or tranny leaks. Started pulling the alternator got the 6 point top bolt off using a breaker bar and pipe. The bottom 6 point not so easy, it is now i slightly stripped. An 11 mm 12 point socket fit fine. Going to go buy a 6 point 11mm before I really screw it up.

Rodm

that reminded me of something, I once went to check a turbo E300D that was for sale, I didnt buy it because it looked like the guy used it as a farm truck, but I did help him out in correctly routing the belt.

He became a good freind

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

Took the alternator which had the following numbers on it 90 AMP - BOSCH 0123320045, MERCEDES 010154702- to Autozone advised it checked out fine, took it to Advanced Auto the same. WHAT NOW???

Rodm

Clean all the ground straps and + terminals between the alternator and battery.

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I did buy a new voltage regulator and replaced it . One of the brushes was black and only had a quarter inch left. I cleaned the + and - at the alternator, The only ground strap I found was under the vehicle from the bell housing to the frame. I removed the strap and brushed it with a wire brush until it was clean (copper colored.) At the starter I was able to see where it connects to the starter and goes to a metal plate. It was not rusted or corroded. The wires are in a plastic cable housing which ends up under the car by the transmission as mentioned before it looked ok however I did not try disconnecting the starter wires and then removing the plastic covering. I checked static voltage across the battery, then from the battery box in the engine compartment to various points in the engine compartment INCLUDING THE - SIDE OF THE ALTERNATOR voltage was the same 12.62 v. Started the car and again no increase in voltage across battery. Is there an inline fuse from the alternator?

Rodm

How long did you wait for the voltage increase. Mine takes a few min of driving before I see peak 14.3v (13.5v on the CCU)

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Miracles do happen. After my last post, went back outside started the car up and began testing with a volt meter to see if I had missed anything. I had my wife rev the engine and immediately the voltage across the engine battery box went up to 13.89 v. At idle it dropped to 12.67. Well will see how long this lasts keeping my fingers crossed. AND THE BATTERY CHARGING LIGHT WENT OUT.

Rodm

The alternator is not fused. However, the alternator's excitation current comes from the alternator lamp in the instrument cluster. If the lamp is burned out the alternator will not make electricity.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970