[HandymanTrainer]

As a factory trained Carrier technician, my first step would be to eliminate any shorts in the t-stat wire by simply removing them all from the control board. Then, with the power to the furnace off, I would use a continuity tester to check from each one of the two terminals the fuse plugs into to ground. If either one shows a short to ground, you know you have a control board that needs to be replaced. If there is no short to ground on the board, then process of elimination sends us to check the stat wires and stat for shorts. IN ANY CASE the five amp fuse located on the control board is strictly for protecting the transformer in the event of low voltage shorts. Never replace a board fuse with any other amp rating then that which is factory installed.

HandymanTrainer