What are some causes of blown fuses in the inside unit of a heat pump? I had a blown fuse in the heat pump, replaced the fuse and the unit worked fine and heated the house up and blew the fuse again after an hour or so. I vaccumed out the inside unit sprayed contact cleaner on the contacts and replaced the fuse again, and the same thing, ran an hour or so and blew again. It's a 5amp fuse and a Payne unit

There is a intermittent short in the low voltage wiring or there is a component that is drawing too much current in the low voltage wiring. Look at the wiring from the house to the unit since that is subject to damage first. If nothing found there then you will have to track it down in the unit outside then inside to the thermostat.