This is in the 240D (manual CC)

It sounds like a pigeon, and seems to be coming from behind the instrument cluster.
Like a whining gurgle? Kind of rhythmic, or maybe cyclic.

When I turn the compressor off it goes away.

Doesn't vary if I turn the compressor control knob up or down - if it is on, it makes the sound.

The speedo seems to dip slightly with each pigeon "coo".

A/C seems to be working, though maybe not quite as well. (It has been converted to 134a, so it isn't ever a freezer.

What should I look for?

__________________

Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

The compressor speed is a function on engine rpm only. I suspect that your "compressor control knob" is actually controlling something else.

It must control the size of the opening that allows cooled air in. The higher I turn it, the colder it gets.

The noise doesn't vary with RPM, only speed.

If I open the throttle in neutral, the sound doesn't occur.

Also, shifting gears (thus changing RPM but holding speed) doesn't change the sound.

If I shift into neutral and then stop the car, the sound fades away somewhere around 35 mph.

__________________

Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

My car kind of makes a whining noise when I have my heater/fan on. If i hit the gas or slow down it goes away but when i settle into another "groove" it will come back on. If i turn off my climate control it goes away completely. I figure its gremlins.

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1963 Ford F100 - Cummins Swap?
1985 Mercedes 300SD - 210K
1992 Ford Festiva - 92K
2001 Ninja 250 - 8K

Gremlins indeed. I get a little flutter, like pigeons or squirrels hiding in there, with the AC on my SL. Intermittent, barely audible, nothing light background music doesn't drown out.

I'm not concerned, yet! Surely someone will post something that will scare the S*** out of me pertaining to this issue.

__________________
1985 500SL Euro w/ AMG bits 130k
1984 300SD Turbodiesel 192k
1980 240D Stick China 188k
2001 CLK55 AMG 101k
2007 S600 Biturbo 149k Overheated Project, IT'S ALIVE!!!

Could be a case of jealousy. Are you dividing your time evenly between your 240d and 'new' 300td?

__________________
1985 500SL Euro w/ AMG bits 130k
1984 300SD Turbodiesel 192k
1980 240D Stick China 188k
2001 CLK55 AMG 101k
2007 S600 Biturbo 149k Overheated Project, IT'S ALIVE!!!

nah....she knows she will always be my first


Seriously, though-could it be due to low pressure?

It seems to be cooling worse than usual - at least I know others have the same sort of noise - though I would need to put it on the metal station to drown mine out.

No noise on the way home tonight, BTW.....

__________________

Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

Is it leaking?

__________________
1985 500SL Euro w/ AMG bits 130k
1984 300SD Turbodiesel 192k
1980 240D Stick China 188k
2001 CLK55 AMG 101k
2007 S600 Biturbo 149k Overheated Project, IT'S ALIVE!!!

I'm not sure.....I have to get a gauge.

It has never cooled very well, but seems to be worse now.

__________________

Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT