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.