Support Article

Fujitsu AC stopped communicating with KNX after a power outage when using an IntesisBox FJ-RC-KNX-1i?

When a Fujitsu AC indoor unit is turned on, it scans its control line for any controllers or interfaces. As this scan is only performed on initial start up, it is imperative the IntesisBox FJ-RC-KNX-1i is powered and has completed its own start up procedure so it will be identified. If the Fujitsu indoor unit doesn't identify the IntesisBox FJ-RC-KNX-1i then communication between the units will not be possible.


If power is applied to both units at the same time, such as after a power outage, it is likely the IntesisBox FJ-RC-KNX-1i will not be ready when the Fujitsu performs the scan. 


There are two ways to overcome this:

  1. Use a KNX PSU with back up batteries for any lines which include the FJ-RC-KNX-1i. This will keep the FJ-RC-KNX-1i unit powered during short power outages ensuring it is ready when the Fujitsu indoor unit completes its scan. The amount of time the systems will remain powered for is dependent on the size of the batteries, number of devices and bus load.
  2. Request the Fujitsu AC installer to include a timer relay set for 1 minute switch-on delay so that when power is restored the Fujitsu unit will not start up immediately, allowing the IntesisBox FJ-RC-KNX-1i KNX to be ready to answer when the initial scan is carried out.


The second method is preferred as it will ensure communication between the two units is always possible, regardless of the duration of the power outage.