the 600VAC rating is the maximum allowable voltage

Encased in a rugged phenolic resin case (black bakelite)

the "U" designation typically refers to universal retail packaging

noisy operation

though you should always verify the specific amperage draw of the compressor against the 9

Resideo Q340A1066 Thermocouple the 600VAC rating is theThe Resideo Q340A1066 is a professional grade Universal 30mV Thermocouple designed for high reliability pilot flame sensing in standing pilot gas fired heating systems. This 18 inch thermocouple features a heavy duty construction with a focus on Maximum Copel content to ensure long term durability and consistent millivolt generation. When the pilot flame contacts the tip, the resulting temperature differential produces a stable 26mV 32mV open circuit