This block appears if automatic controller can control compressor. This may be only automatic controller for dehumidifying dryers.
Depending on the number of compressors defined in the system, one square will be shown for each compressor. If the box is empty, the digital input for the compressor is not active, i.e. the compressor does not work. If the symbol x is shown in the box, the compressor is switched on and working confirmation is sent to the digital input.