Greetings All,

This may seem like a dumb question, or perhaps not, but here goes. Seems that my idle speed is too low on my '79 300D engine to turn the a/c compressor while sitting still in park without the clutch howling and squealing to the point that the compressor won't turn but the belt will. Raising the idle a bit seems to solve the problem, the clutch stays engaged, the belt turns fine and all is well in a/c land. But if you shut off the a/c it just seems that perhaps the idle is a tad to high. I don't have a calibrated ear or anything, but is the normal rpm of the engine unloaded continous sounding or that clacky, clack sound? Raising the rpm slightly seems to make it all go away. I always thought a load on a diesel engine really wouldn't make an impact on dropping rpm, but it does. Is there some adjustment besides raising the idle speed I'm missing, or is it just part of an engine with 164,000 miles on it saying give me more fuel if you want more work out of me. Perhaps the compressor, York type, is going bad. Tell me what you think.

Charles

Replace the belt and tighten it firmly! The noises are all from the belt.!

__________________
Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS

Greetings,

I think there is probably enough tension on the belt as it is now and the problem seems to be not enough RPM to keep the engine turning suffiently to keep the compressor turning as well, it seems to squeal at a real low RPM. Any tips on how to set the RPM by ear and be close to the proper unloaded setting?


Charles

It should not change that much. If the pressures are OK and the auxillary fan is working, you shouldn't have to change the idle. If the belt is new and properly tight, you will not get any squeal..IF you did, it would squeal every time you shut down the engine.

To raise the idle, there is a 14mm nut below an adjustment screw on the side of the injection pump. IF you loosen the nut and turn the screw clockwise, it will raise the idle.

__________________
Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS

Greetings Donnie,

I guess I really had the engine RPM set to low to allow the a/c to rotate at the proper loaded speed. Raising the idle up a tad really seemed to help to keep the clutch and compressor turning at idle. Is there any easy way to tell what the rpm is on these diesels without having a calibrated ear? I can generally set the older gas engines by ear, but these MB diesels are a bit trickier.

Thanks,

Charles