Air was working fine and set it to 82 leaving. Net day the system didn't work wouldn't run fan or air from the thermostat. Is a m1mb 077a unit. Found that the 3 amp fuse had blow and replaced it the fan ran fine.. placed it in air mode and it blew the fuse again. Help.

You have a problem with the 24 volt low voltage control circuit. Check the low voltage wires going to the outside unit first. Could be a shorted coil on the contactor also. Post back with results.