Performed AC diagnostic on one-year-old Lenix condensing unit. Upon my diagnostic I found the thermostat downstairs was completely blank. I then proceeded to the attic to check the incoming 120 V coming from the breaker and found that there was no power supply present. Upon further investigation found that the outdoor breaker was not in tripped position although not supplying power, flipped breaker and 120 V energized furnace and system is fully operational and cooling. Upon conclusion I believe that the breaker could be potentially weak or that other things may be tied into the circuit of the furnace and electrician should evaluate the breakers.