1997 C230: Moaning Noise When Climate Control On
 

My 1997 C230 is acting up. The car, very well maintained with 95,000 miles, drives and operates fine (including cooling function of the climate control), but, when I turn on the climate control, there is a periodic, moaning noise coming from the engine area.

I ran a few tests (standing still, engine at operating temperature, outside temperature 60 degrees Fahrenheit) using the pushbutton control module and, as it relates to the periodic moaning, here’s what I saw:

Codes 05 (evaporator temp) and 07 (AC pressure) were fluctuating as the moaning noise came and went.

Specifically, when the evaporator temperature climbed to 41 degrees Fahrenheit, the moaning noise started. When the evaporator temperature declined to between 39 degrees and 35 degrees (I tested the pattern for about ten minutes), the moaning noise stopped. The time interval between the moaning coming and going was about twenty seconds.

Further, following the same time cycle, when the AC pressure declined to 22 Bar, the moaning noise would start. When the AC pressure climbed to 26 Bar, the noise stopped.

There were no fault codes stored in the Diagnostic Trouble Code Memory.

In short, the moaning noise coming and going seems to be directly related to the fluctuation in evaporator temperature and AC pressure.

Can someone tell me what’s wrong?

Thanks in advance.

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