﻿In standard commercially available fan coil units, there is generally a distinction made between two different ways to control the fan levels via relay outputs. Which of these two principles has to be used should be obtained from the technical documentation of the connected fan coil.

*Only one fan output switches (change-over principle)*: As soon as the fan is running, there is always only one fan level output switched on. All other non-active levels are switched off.

*Fan outputs switch hierarchically (level principle)*: The fan level outputs switch in sequence (hierarchically) when the fan is switched on. All fan levels lower than the active fan level remain switched on, higher ones switched off.

When only one fan level is used, this parameter is always set to "only one fan output switches (change-over principle)".
