If your thermostat is blank, that means there is no power going to the thermostat. First, replace the batteries on the back of the thermostat. If your thermostat’s display is still blank, check the power switch of your HVAC system located by the indoor furnace or AC unit which is usually located inside the mechanical closet or in the attic (if your indoor unit is located in the attic). The last thing that can be checked prior to calling our AC repair service is the breaker in your breaker panel, as well as the breaker located behind your outdoor unit. If you are still experiencing a blank thermostat after checking the above-mentioned items, give your AC repair company a call to schedule a diagnosis. If the issue is not related to equipment failure, you might have a clogged drain line that tripped your emergency float switch.