Why is my new Trane circuit board keep blowing fuses ?

You have a malfunction or unsafe condition that has to be found and corrected. Highly recommend a certified tech to trouble shoot your unit, as you will need a multimeter/ohmmeter to track this down. That may save you the added expense of just changing out parts until you find the one causing your issues.

Otherwise you must provide a lot more information like make and model number to download a trouble shooting manual, or interpreting your LED error lights, if applicable.