This morning when we ran our a/c, my husband noticed that the fan was blowing but the compressor wasn't kicking on. He changed the thermostat and now nothing turns on, not even the fan. What should we check first? Thanks :)

The thermostat is at fault about 2% of the time when the system is not working correct.If nothing is working now the thermostat is wired wrong or a low voltage fuse was blown or transformer when changing out the thermostat(if power was not turned off first going to the fan coil or furnace). If you can give us more info of the system it will help. What brand, gas furnace, heatpump and around the age of the system?

It's an electric with a heat pump, York, and is about 6-7 years old. Thank you!

Where is the relay fuse located?

The secondary low voltage fuse is located on the fan control board inside the fan coil unit(indoor blower section). It's a simple automotive fuse five amp or less, replace with same size fuse.