Customer stated rooms on left side of house were not keeping up. Noticed alert on thermostat for batteries and temperature sensor. Last time I was here customer was unable to find the temperature sensor, so I advised them to replace the batteries at their convenience when they find it. Upon inspecting temperature sensor for the right side of the house I found a large amount of corrosion on the terminals, preventing a good connection. I then cleaned off the corrosion from the terminals and replaced the batteries. No errors were found on the thermostat after replacing the batteries and this should help. Keep the temperature balance throughout the home a lot better. I then tested to ensure the compressor was running at full capacity and the heat kit was still working as designed. Found no issues with the heating cycle. Suggested to homeowner if temperature balance does not improve on the left side of the house that they may need another temperature sensor to ensure a better balance. Left