I am having a problem with our heat pump. The last 2 days we have noticed a burning smell downstairs and were trying to locate where it was coming from. Narrowed it down to the heat hump. Vacuumed the unit out and replaced the filter yesterday. This morning had the same problem. Seems to happen first thing in the morning when the unit is coming on to warm up after being set to a lower temp over night. This morning the unit stopped working and I checked the fuses. It has two fusetron fuses for the heat side of the unit. One of them was literally burned up. Have never seen this before. Have blown fuses before, but not seen them disentigrate into dust particles. Should I replace the fuse and see if it happens again or just call the repair man? Was wondering if there could be a problem with the secondary heat strips causing it? Scared of having a fire now. :confused:

I would check the secondary heating strips carefully. If you have an ohmmeter, see if they have the rated resistance and are not shorted to ground. Also make sure the fuses and wiring are heavy enough to support the secondary heat strips, fans, and the compressor. The compressor should give the amps it draws. The wiring should give its size on it. 10 ga wire is good for 30-40 amps. The wire is undersized if it gets warm to touch. Check the fan and blower motors. A dry bearing could be causing a higher power draw. If you don't find any problems, try new fuses. If there is a problem, the fuses saved you once, and should again. If they blow again, better call a repairman.

In addition:
If the fuses were "disintegrated", or "burned", then you should also inspect for poor mechanical/electrical contacts in that area (check that the fuses are firmly seated, clean the contacts if they look dirty). Fuse contacts are not designed to heat up and will eventually "burn-in" when they become resistive.
Then you come to the stupid situation that what is protecting you against fire, might cause fire (OK, OK, maybe this is an overstatement - but I could not resist).