Amazing to have joined the board just in time to post the first question on the Heat Pump Forum.

I have an 18 yr old Trane heat pump with a 21c140501 defrost control board. The outside fan will not run. Using multimeter I have determined that the NC relay on the DFC board is open. Haven't determined yet whether the relay is bad or something in the defrost control is calling for the fan to be stopped. The red led is flashing three quicks and a pause. On my other units the led gives a steady flash. I presume that is an error code.

I jumpered the relay out of the fan circuit and the unit appears to be functioning normally. I will need to repair before heating season. An new OEM board is $360 so I really would like to know if I need it before shelling out the bucks. Any advice on troubleshooting would be appreciated.

Regards, Ed