I worked on this unit for the last few days. I came in and replaced a blown fuse. Unit ran for a day. Now the fuse blows instantly as soon as power goes to unit on both cooling and heating. I disconnected ever wire but the c to the t stat then when I try to add the are power wire it blows the fuse instantly. I can't find any evidence of damage to any of the wires in the air handler. I ran new t-stat to the thermostat but didn't help. Tried to put in a new circuit board and transformer and no help. I am out of ideas I have changed everything on the low voltage side in the airhandler I can think of.

If the Blower motor relay coil was shorted, it could do this as it is common to both heating and cooling.

I was tripping the fuse with the g wire disconnected from the circiut would that still cause it to blow with no signal to the fan to run?