Goodman Model GPC1242H41CA Blowing Low volt fuse ONLY when heat is turned on
My guess is there is a short in either the W wire or in one of the heating components. If it happens immediately it is probably in the W wire. If it goes for a while it is probably in one of the components and when that component is energized the fuse blows. Try disconnecting the thermostat wires from the unit and jump R to W. If it works your problem is in the thermostat or thermostat wires. If it stil blows the problem is in the unit itself. They do make things called poppers that are basically circuit breakers instead of fuses that fit where automotive fuses go. Saves a lot on fuses when not sure where the problem is.