HVAC Fan Running

Many of these stats use pretty small relays which can become welded contacts, and some use solid state devices like transistors or SCRs and those can fail

One time a service call, complaint was "no cooling." This was a one time customer and we had not installed the system so I was unfamiliar. Before I entered the office building, I checked the 5 OD units and was unsure, because not all were necessarily "calling." But one the suction line was VERY VERY warm, and it was not a heat pump!!! Turns out the office people had bought a bunch of cheap import "setback" stats and one had failed, bring BOTH heat AND cooling on at once!!! The furnace was heating and the AC was "trying" to cool!!! LOLOLOL