Installed New Thermostat Ac Not Working . If nothing seems to work, it may be time to upgrade to a new and improved thermostat. One subtle sign of a broken thermostat is when temperatures in different rooms do not. Installed New Thermostat Heat And Fan Work, AC Compressor Wont Turn On from www.diychatroom.com The best price i have got so far for the 2 x xv80 furnace(60k and 100k) + xb13 ac + 2xtrane 602 thermostats is $8200. If you check these and all is in order then read on for other solutions to ac problems. I bypassed the thermostat to confirm the unit was working and it indeed came on.