My '95 E300 Diesel's idle speed varies based on whether the AC compressor is engaged or not.

With the car in PARK, and the AC compressor engaged, the idle speed is around 600 RPM, however with the AC OFF, the idle speed goes-up to around 900 RPM.

When the car is in DRIVE but idling, the idle speed is constant at around 600-RPM. This is irrelevant of the status of the AC compressor.

Is this normal?

Thanks

Phil