Nest Thermostat

I recently purchased a Nest as a gift for my Daughter since I own 2 in my house and love it. Unfortunately, installation for them didn’t go all that well. Everything appeared to be working but then we noticed the blower doesn’t shut off even when the a/c is off.

After verifying compatibility on the Nest website and reviewing all the wiring is correct, we reinstalled the old thermostat only to discover the same problem. A problem that wasn’t there before installing the Nest.

This suggests installing the Nest somehow damaged circuitry in the a/c unit since it worked properly previously.

Now we’re attempting to troubleshoot the a/c with the original thermostat. Bottom line is the blower no longer shuts off.

The components in the unit are a control board, a 24 v transformer and what appears to be a solid state relay. Obviously, we don’t want to start replacing components randomly with no understanding of what might be damaged because of cost.

Can anyone shed light on a problem like this? Particularly some insight on what might be in the relay, but the problem over all?

Somethings dead like you suspect but have no ideas to help except to say there are some very good HVAC forums just like here you can jump on and post your issues and what you know so far and I bet a pro will give you a fix or proper trouble shooting advice so you don’t have to start replacing everything.
I had to replace the crossover pipe under my house and the 90 degree elbows that were rotted out that connect it all together and I just did a search and found several sites that had good info on what parts, tools, and tapes to use to do it though I do have some experience doing duct metal work and all that.
I replaced the thermostat here with a 7 day programmable and had some issues with the fan running half speed when the heat kicked in and found the solution on the forums too, plus it was buried in the users manual as well, but luckily my fan circuit wasn’t damaged, just not set right in the advanced setup of the new unit. I just Google’d my basic issues ands several forum posts came up among other things that helped me both times.