One hot Summer day, My Central Air went out, but the fan continued to run even when the thermostat was turned off. The smell of burnt electrical wiring throughout the house. I removed the front cover of the air handler, unplugged the 120 VAC power cord and When I checked the circuit it was obvious that the 24 volt transformer had burned out. I replaced it and included a fuse in the circuit. I also discovered that the wires going to my outdoor ac condensor unit had been shorted by the gardeners weed wacker. After making a repair and installing a conduit to protect the wires from future damage the unit appeared to run fine. The following day, after working for a short period, I have been informed by my wife that the unit is not working. I rechecked the fuse and the transformer output. All seem to be in working order. Any suggestions about what to check next?

labman

I would go back over the wiring you repaired. The fan should have quit when the transformer fried. That suggest problems in the furnace controls. Unfortunately, the newer furnaces have them on a circuit board, more difficult to trouble shoot. Thus, when a relay goes out, it is easier to replace the $300 board, than verify it is the relay and replace it. the relay to the compressor and its fan is a stand alone unit easily checked. If you have power to the coil, but not the load side of the relay, the rely is bad.