My Heil HVAC keeps blowing the 5 amp fuse. I have replaced the indoor circuit board (OEM), the capacitor, the 24v transformer (OEM), and the thermostat. I am about ready to replace the thermostat wiring in hopes that it is a continuity problem that's causing the fuse to go, but the unit works fine for approximately 2-48 hours before blowing.

The home (I believe) experienced a lightning strike back in the summer, which (HVAC-wise) blew out the indoor circuit board, the transformer, and the obvious 5 amp fuse. I was deployed at the time and can't confirm. (As I was trouble-shooting the unit, I saw the arc mark behind the circuit board on the mounting panel). Again, the unit will run for anywhere from 2 hours to 48 hours, but then the fuse will blow out again. The electric company has replaced some problem wiring on their end (transformer to the home attachment), but no success with my unit. All other circuits in my house seem to work properly.

Semper Fi

Can you give a model number? I can not find any schematics for any Heil a/c. If you have one is there anyway you could scan it maybe? From what I can find, it seems that that fuse protects the circuit board. If it is blowing it seems like it is a problem with one of the major components i.e. compressor going bad or fan etc... Have you been able to find out what exactly will cause it to blow. I.e. when the heat is on and not the cool or when the fan is switched to maunal on. Does the unit make any strange noises? Has it been serviced lately? Refrigerant and what not all good, no dirt or bug nest in the wiring?

Have you checked for scorched wiring? There could be a wire that is burnt and either shorting or just causing it to draw too much resistance and blowing the fuse.

A schematic would help a lot.

Heil NFCX3600C2 is the model number. I'm working taking pictures of the schematics on the unit, but I need a few to get them on this blog. The unit itself works properly for about 2-3 hours now, but then blows the fuse. I will check the manual cool and fan to see if this blows the fuse, and it was serviced back in early summer of 2010. I check the wiring bundles for continuity &/or arcing and they all check okay.

How do we upload the schematics on here?