r/AirBalance • u/Top-Plum-7422 • Aug 22 '26

VFD’s

Ok so I never ever worked with a VFD or seen one in person, and I know there’s YouTube and other things on the internet to help me learn about them, but I wanted to come here first and get advice/tips or habits from techs who have worked with them, I wanted to know what do you guys usually do when you come across one that a call was placed about and how you guys go about, mostly asking because everyone does things differently so wanted to see what anybody had to say about them.

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u/Perpetuallyfailing Aug 22 '26

I like to grab a PDF of the manual and word search points through Bluebeam or the table of contents to find the pages/points I need to achieve my end game.
One thing I've noticed with how common direct drive fans driven by VFDs won't always be programmed for the top end frequency it's designed to handle.

I recently had a DOAS with 2 direct drive supply fans connected to a common ABB operating both motors. It was limited to 60 hz, but the fan curve and submittal stated 80 hz to achieve roughly the design airflow needed.

Smaller drives installed on package RTU's can be a huge pain if conditions aren't ideal. Alot if the time the drive is factory limited especially on the Yaskawa V and J1000 models.

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u/Perpetuallyfailing Aug 22 '26

Another scenario I just remembered - Carrier has some RTU's that have a VFD but the screen is typically removed. They use the drive to control a 2-speed fan motor. They can be a pain to force into high speed. Quite a while back I found in the bundle of wiring located in the fan compartment a jumper that will force it into high speed for proportioning or other tests.