That unit uses many relays in various circuits, they become unreliable after a period of time. Most failures usually occur when the unit is hot. If you have knowledge of electronic service, you might be able to locate the bad relay or component with freeze spray. If you don't have service knowledge, I recommend you contact Spectral directly. You could see about a repair facility that has experience with that unit. Some people on this forum may have a suggestion for a service shop if you mention where you are located.
Why phase reverse switch only works when cold?
On my Spectral DMC20 phase switch only works when unit cold. In recent heat wave (104-113 degrees) I turned off electronics fearing ac failures. When I turned on today discovered phase reverse works when the unit is cold. After warm up switching again gave silent in reverse position?