Squiggle, the door switch interrupts power to the hi-voltage/maggie units. 20A is a lot of current. Blowing this up only when the door is closed indicates a short circuit somewhere in the high power usage circuitry. Did you try using your ohmmeter to see if the resistance from the line voltage wire to ground is low when the power is disconnected? (Be careful when working around the HV circuitry; the capacitors - which could be the problem - can zap you even when power has been removed for some time.) Start disconnecting things until the resistance goes up appreciably. (Note: I don’t have one of these particular units, so this is just general advice, not specific to your unit.)