new thermostat created a short at the air handler

Help....

I have one of the old mercury thermostats (Janitrol HPT 1860) and wanted to replace it with a digital thermostat. (Honeywell RTH2410B) So I followed the directions, flipped breakers off and terminated the wires. I flipped the breaker back on and tested it. Fan On - worked. Air Conditional works. When I switched to "Heat" - something at the air handler "blew"! Nothing worked anymore.

I realized what I connected the "Blue" wire on the new thermostat at "B"! Wrong thing to do......?



I hooked my old thermostat back up and nothing works. No fan, fan compressor, no heat. This is a Goodman AW24-05C system in a condo, all electric. I can't find a low voltage fuse.... can't figure out what blew....

Can Anybody help?

Thanks

new thermostat created a short at the air handler