Blower Override Switch: Description and Operation

COLD ENGINE LOCK OUT SWITCH (CELO)
The Cold Engine Lock Out Switch (CELO) has the function to prevent blower operation when heating is required and the engine coolant temperature is below 120° F. When the coolant temperature exceeds 120° F, the CELO switch opens, turning the blower on when heating is required. The CELO will not prevent blower operation when cooling or defrost is required.