where in the furnace does it say if it uses a 3 amp or 5 amp fuse for the circuit board? Or how would I know which is correct
If the thermostat is relatively close a 3 should work. Further away use the 5. If the 3 blows try the 5. If the 5 blows, you have a problem in the furnace.
It's usually indicated on the board itself as a consequence of the manufacturing process
look closely just behind the fuse 3A 2www.amazon.ca
It should be documented in the service manual but this is a easier way to confirm. If you can't determine the size, always go with a 3A fuse. The difference between 3A and 5A on a circuit board is very significant. And a short on 3A board using a 5A fuse is very likely to blow a component.