Found system operational upon arrival. Customer said thermostat gave out error code “critical’. Checked system and found no saved error codes. Checked electrical and freon pressures. Everything was within range. Customer said unit only had that error code once and then it went away. No repairs done today. Unit operational upon departure. 1. Recommend adding extended warranty to cover labor, freon, and warranty processing. 2. Recommend surge protection for air conditioner. Customer declined recommendations today.