It felt like I blew a fuse when I changed thermostats this morning and now neither my old thermo or new one work. I just replaced the transformer, still nothing. Fuse makes sense, just trying to find it.. any help

Should be in that air handler somewhere on the low voltage wiring. vid of one here.

https://www.youtube.com/watch?v=yiy_Gxb_9JI

I have seen many with no fuses. If so, check for 240 Ac volts to the Primary of the transformer, and 24 Volts Ac Out of Transformer and follow the wires from transformer for any fuse.

Man, that is so true. There are some without.

I guess when you 'think' you popped the transformer did you hear an audible pop and that electrical smell with it? That would be the giveaway that there is no fuse. When you get it squared away I would put one in the system. They are a lot cheaper than transformers.

Just a note,, don`t look for 240 ac volts if you have a gas furnace,

Good point, and if your transformer has multiple wires for the primary side make sure you are using the 120v you are bringing in for the furnace..