It's not a variable displacement compressor. MB did not adopt those until much later. The SDL uses a Nippondenso 10P15c. It's a very good little compressor, but it has two modes - on and off.

It's normal for the compressor to not cycle on warm days - say anything much above 85 degrees. Does it cycle at night, when there's no heat load from the sun? That's a better test.

- JimY