Arrived on site to perform AC diagnostic on Lennox system. Upon arrival homeowner states that zone two is no longer active on the S30 thermostat. Proceeded to upstairs to verify the thermostat was an active and found no screen being displayed at this time. Remove thermostat off the wall and tested for power and found 12 V DC present at thermostat. Re-insert thermostat on the wall and it came back online. Verified and tested system and ran it for approximately 20 minutes and no issues occurred. It appears the thermostat may have been loose on the wall or possibly banged causing the imperfect connection were it lost power. Cycled system five times and system ran fine with zone disconnection. Upon departure system is fully operational and cooling