[RaiderZA]

I was in my basement tonight where my furnace and blower unit is located. I heard a small click and saw a flash of white light out of the corner of my eye. Not knowing what it was I inspected the furnace, water heater, etc. I then noticed that the air did not kick in. I checked my bnew Carrier thermidistat and noticed that it was flashing the cooling mode because the house temp was higher than the setting, but the AC did not kick in. I switched the blower fan button on the stat, and the fan in the basement unit worked, but no life from the outside unit. Is the non working AC related to that flash I saw? Did a fuse blow somewhere? I notice that the stat wires congregate on a metal box that has a note about a time delaw 15A fuse. Is that blown? The circuit breakers appear OK.

[labman]

The 15 amp fuse likely is the main one for the furnace. If it blows, nothing should work. Open the box and see if you have 24 volts between the B and Y terminals when calling for A/C. If so, check to see if you do at the coil for the outside unit.

[RaiderZA]

Thanks for the insight.
Do you think the white flash I saw is a result of a fuse blowing in the A/C? Or is that something likely more serious?

[labman]

I am at a loss to explain the flash. Furnaces often have a fuse on the incoming power. Better ones have a smaller one protecting the control transformer. If either of those blew, the blower wouldn't work. The only A/C fuse would be outside in the disconnect at the compressor. Somehow the yellow wire from the thermostat or one of the pair running from the Y and B terminals to the compressor coil could have burned in 2.