My dad has a heat pump, when the heat is turned on the 3 amp fuse on the 24V red wire off the transformer is blown, a/c is fine. The transformer was replaced, the blower contactor reads 10 ohms across the coil, the backup heat contactor reads 15 ohms. Both work when contactor is pushed in.

Someone told me that one would check all the low voltage wires to see if they are shorted. Does that mean one would disconnect the wire at both ends (at the thermostat being one end) and then check it to ground, hoping to read OL? Since it's the heat not working, either the white or red wire would be shorted, correct?

Could it also be a motor problem?

I'm only a few months deep in this trade and I'm curious.