So I moved into a new house that I’m renting and wanted a wifi thermostat to monitor temps in the house because I work out of town and have animals at the house. I bought a Honeywell T5 thermostat. Most of you know it’s the style that’s just a faceplate that snaps onto the base.. this is the reason I was comfortable changing it because I didn’t have to mess with any wires because the one that was installed when I moved in was the same but not the wifi version. So I shut off the breakers, pull the thermostat face plate off, snap on the new one, and turn the breakers back on. I turn on all the functions and everything works great (including the AC). For a week we use the heater, everything is fine. Friday comes and I’m at work and see that the temps are getting warm in the house. I turn on the AC with my phone and it works great for an hour. Then I get a notification that the thermostat lost connection. I figured maybe the internet went out. I come home three hours later to find no power at the thermostat. Breakers are all on..found the fuse at the furnace panel was blown. Replaced it and the fan worked but no AC. The unit on the side of the house was not kicking on. Property management said they would send someone out but it would be two weeks. I did some troubleshooting and found very old fuses at the unit outside and replaced them for piece of mind. More testing and found out that the contactor plunger was pushed out.. figured that it was probably bad. Well the HVAC guy showed up and I stupidly told him that I changed the thermostat. I tried to explain him what led up to all this to help him diagnose and he just told me that I was liable for any bill..had a terrible attitude from the second he walked in the house..anyways he found the contactor to be bad and charged $300 that I’m now stuck with paying. Did I do something wrong to fry the contactor or was this just bad timing? Both furnace and AC unit are less than 5 years old. The hvac guy said he installed them.. I have no issue paying for something ing that I screwed up but I don’t see how it was my fault..

TLDR: replaced thermostat and it led to a blown contactor?