| 摘要 |
PURPOSE:To provide a control method for a heater circuit which detects a wire breakage and short-circuiting of a heater circuit to perform a phase control by using a switching element, and also performs a failure diagnosis including a phase circuit control signal part. CONSTITUTION:A phase operation is performed by a triac 2 for a set period of time after the start of a power connection to an auxiliary heater 4. A current value at that time and a previously set current value are compared by a current transformer 3 which detects a current flowing on the auxiliary heater 4. When the detected current value is large, and the current value does not change even when a phase control is performed, a judgement for a short-circuiting, etc., of the triac 2 is performed, and a failure diagnosis for the heater circuit including the triac 2 is performed. At the time of deficiency, a magnet relay 1 and the triac 2 are put under an open mode, and power connection to the auxiliary heater 4 is stopped, and the temperature of the auxiliary heater 4 is prevented from abnormally ascending.
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