Yes.. hopefully they are 'labeled' properly.. check that one... sometimes older fuses will fail. DC circuit may be weak..
-Check for proper voltage... if voltage low, check that and resolve if not correct. (+12.5VDC).. it is possible the battery (12VDC) supply has a problem...
Try ONE more fuse... PROPER value!! do not 'increase' the size!!!!
If it fails, you have a wiring / furnace part failure. In my experiences, the highest 'load' is from the 'fan motor'... Check that it is 'free' spinning... bugs or vermin can get in there and nest in the fan blades... the 'start' load could 'blow' the fuse (the fuse is there to protect.. right?)
Here is a possible sequence...
- Shut off furnace..try unplugging all of the wires going to the furnace AND all parts inside the furnace (fan and solenoid).. Ensure the power wires are secure on the fuse panel... then replace the fuse.
.... If fuse blows, your problem is likely somewhere in the wiring.. most likely where the wires enter the furnace...
.... another possibility is that wires inside were chomped on by something...
- Hopefully the fuse will not blow. If it doesn't, turn on the Furnace control (thermostat)
.... fuse blows? disconnect the thermostat and check for 'short' to ground
- If thermostat and wiring appear to be OK...
.... remove fuse, turn off thermostat, plug in the 'control board'... install the fuse and turn on the thermostat.
.... If fuse blows, problem may be in the 'control' board of the furnace (shorted, damaged).. if so, replace the board.. recheck..
- If fuse doesn't blow... check for damaged/shorted parts in the furnace... motor, gas valve solenoid....
Let us know how you do..
Peace and Blessings..