I have an 120 ton Intellipak II. It has a VFD drive (TR1) on the return fan and the supply fan. About 2 months ago I got a call that the unit was not running. I found that the unit was alarming "Return Fan Failure." The VFD display was showing the fan running at 30hz and the warning and alarm lights were flashing. The display to the unit was froozen so I could not view what the alarm was or do anything with the drive. I tried pushing every button and nothing happened. I stopped the unit on the HMI but the drive did not reset. I had to disconnect the power and let the capacitor drain. Once I turned the power back on everything was ok and the unit ran. There was not history of the alarm though besides "Return Fan Failure." I didn't think to much into this problem until it happened again yesterday. Now I am wondering if I have a faulty drive or fan motor or possibley something else. I am planning on switching the VFD with the other RTU to see if the problem follows the drive or stays with the unit. I am curious if anyone else has had this problem with these VFD's or with the Intellipak II and what the cause of it was.