A USF fault (fault 22 on the touchscreen) is a supply undervoltage fault. The VFD detected that the input voltage is too low for the drive specifications. There are three possible causes for this:
1. The supply voltage is too low for the drive rating, for example if 120V is being provided to a 240V drive.
2. There was a momentary power loss. If the proper power has been restored, this fault code can be reset to resume fan operation. If a fan is being run on a generator, this is not supported and can cause many issues. The fans must be be on permanent building power.
3. There is a loose or missing wire on the input of the VFD. Verify that all wires are properly connected to the disconnect switch, the fuse block, and the proper input terminals on the VFD. Verify that the disconnect switch is assembled properly.
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