Interesting one today, unit was running when I arrived as the maintenance guy reset it. Found no superheat, adjusted both TXV's (2 stage evap) to maintain 7ish ⁰F at the evap. The air handler uses a VFD, the call for fan and 10VDC signal come from the condensing unit. When the air hanlder is shut down, and turned back on, the fan won't start even though the VFD displays Hz 30Hz for no call for cooling, 45Hz for 1st stage and 60Hz for 2 stage cooling. But nothing and the compressors will start without the fan. If I shut down the condensing unit or break G for a minute the "Stop" led on the VFD changes to "Run" and there it goes. It's acting like it's almost meant to run this way... Anyone seen this before?

Posted by HVAC Know It All at 2021-06-09 22:24:52 UTC