If you’ve read our blog for a bit, you will have most likely realized that many of our topics come from the inquiries of customers and partners. Instead of helping just one customer at a time, we developed blog posts in order to share simple solutions to common HVAC issues.
Recently, a customer contacted us asking about an issue they were experiencing with their VFD. In their case, their VFD system would only start after a power cycle. Then, before running for some time, the VFD would ultimately stop once again – not good.
In utilizing their system, they had been starting the drive with a contact closure on digital input 18, but also had the VFD connected over BACnet.
In this case, where both communication and hardwired points are connected, it is possible to get multiple start or stop commands conflicting. This can result in unreliable start and stop behavior on a VFD system. This happens when the BACnet BV start point is placed on a graphic or in the schedule, while the BO is also scheduled or commanded.
If you’re also experiencing this issue with your VFD system, here are some steps on how to remedy the situation and in order to have your VFD running smoothly once again.
In cases where the VFD is only going to start using the hardwired point:
Set parameter 8-01 “control site” to “[1] Digital Only”. Now BACnet commands to start or stop the drive will have no effect, only the hardwire digital point will work.
If this does not rectify the issues you are experiencing with your VFD, please feel to reach out to our team directly. Here at AirReps, we have a team of experts who are always ready to assist when it comes to all things HVAC.