Heat worked fine all winter. Turned on A/C and blew a fuse. Replaced 3amp fuse and worked for a few minutes and blew another fuse. Checked all connections, filter, obstructions, need help...

Check its transformer so that you will know its fuse size

That unit has a thermostat I believe and 12 or 24 volts to power it. The 3 amps tells me it may be either line or low voltage, see manual. the fuse blows due to a short in the control circuit, a transformer if low voltage.

Check the blower motor speed control resistor, and all connections for good fitment.

starter overdrawing perhaps

you may of caused a short in the connections or it got moisture why in storge if so the hole subwoofer is screwed

double check your wiring. R terminal on the furnace will provide 24 volts to the t-stat. W terminal in the t-stat will send 24 volts back to the furnace W terminal to turn on the heat. G terminal in the t-stat will send power to the G terminal in the furnace when the t-stat is switched to fan on. Y terminal in the t-stat will send power to the Y terminal in the furnace which in turn will send 24 volts to the A/C outside. The C terminal in the furnace should be connected to the c terminal in the A/C outside as well as to the T-stat. Check the fuse again

Sounds like the breaker tripped, either in your breaker box or in the shut off switch located next to the outdoor condensor. This could be also either one or two of the fuses blew and need to be replaced

The reason why fuses blow is that the current is too much. Is the fuse rating according to the specs ? If yes then ... One or more output power transistor (or audio power IC) may be shorted. have it checked before replacing another fuse as this might cause more damage.