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Troubleshoot ACX781 controller or AC1 IOU module communications.


An ACX781 controller or AC1 IOU module keeps locking up and going offline. What can be done to determine why this is happening?


  • ACX781
  • AC1 IOU module


The most common cause of communication problems is electrical noise getting to the controller.


  1. Rule out any kind of hardware failure
  2. The most common scenario resulting in electrical noise and controllers going online and offline is that there are no 39v MOVs installed at the door strikes. The reason for needing these MOVs is that when the door strike relay de-energizes it creates a field collapse electrical spike that can travel back down the output wiring to the controller. When this happens, it generally will not damage any of the hardware in the controller but it could cause it to reset or cause its memory to get scrambled.
  3. Generally a reset and reload of the controller clears out the problem.
  4. It is strongly recommended to put MOVs on all outputs that have relays on them.  Put the MOVs at the end device and not the controller end.
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Last update:
‎2018-09-06 03:01 PM
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