| 摘要 |
PURPOSE:To prevent a pump from freezing by applying a current to a main coil only when a temperature below a specified value is detected under the condition where a pressure switch is off and a flow rate switch is off. CONSTITUTION:If a temperature detected with a temperature sensor 22 is determined with a low temperature detection circuit 23 to be below a specified value when a pressure switch 18 is off and a flow rate switch 19 is off, a first switching circuit 5 is phase-controlled and a second switching circuit 6 is turned off. This makes a current not to be applied to an auxiliary coil 3 but to a main coil 2. This keeps warmth at a certain temperature due to heat generated with the main coil 2 itself of prevent freezing from occurring.
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