[变频空调维修]-第6章-通信故障-第7节-室外机通信电路分压电阻开路,室外机不运行

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第7节 室外机通信电路分压电阻开路,室外机不运行

故障说明

海信KFR-26GW/11BP挂式交流变频空调器遥控开机后,压缩机和室外风机均不运行,同时不制冷。图6-39所示为室外机通信电路原理图。

图6-39 海信KFR-26GW/11BP室外机通信电路原理图

图6-39 海信KFR-26GW/11BP室外机通信电路原理图

1.测量室内机接线端子通信电压

如图6-40所示,首先使用万用表交流电压挡,测量室内机接线端子上1号L相线和2号N零线电压为交流220V,说明室内机主板已向室外机供电;将挡位改用直流电压挡,黑表笔接室内机接线端子2号N零线,红表笔接4号通信SI线,测量通信电压,正常值在待机时为稳定的直流24V电压,在室内机向室外机供电时变为0V—24V跳变电压,而实测待机状态为直流24V,遥控开机后室内机主板向室外机供电,通信电压仍为直流24V不变,说明通信电路出现故障。

图6-40 测量室内机接线端子通信电压

图6-40 测量室内机接线端子通信电压

2.故障代码

取下室外机外壳,观察到室外机主板上直流12V电压指示灯常亮,初步判断直流300V和12V电压均正常,使用万用表直流电压挡测量直流300V、12V、5V电压均正常。

如图6-41所示,查看模块板上指示灯闪5次,报故障代码含义为“通信故障”;按压遥控器上“传感器切换”键2次,室内机显示板指示灯显示故障代码为“运行(蓝)、电源”灯亮,代码含义为“通信故障”。室内机CPU和室外机CPU均报“通信故障”的代码,说明室内机CPU已发送通信信号,但同时室外机CPU未接收到通信信号,开机后通信电压为直流24V不变,判断通信电路中有开路故障,重点检查室外机通信电路。

图6-41 室外机模块板和室内机显示板组件报故障代码为“通信故障”

图6-41 室外机模块板和室内机显示板组件报故障代码为“通信故障”

3.测量室外机通信电路电压

如图6-42所示,在空调器通上电源但不开机即处于待机状态时,黑表笔接电源N零线,红表笔接室外机主板上通信SI线(①处),实测电压为直流24V,和室外机接线端子上电压相同。

图6-42 测量室外机主板通信电路电压

图6-42 测量室外机主板通信电路电压

红表笔接分压电阻R16上端(②处),实测电压为直流24V,说明PTC电阻TH01阻值正常。

红表笔接分压电阻R16下端(③处),正常应和②处电压相同,而实测电压为直流0V,初步判断R16阻值开路。

红表笔接发送光耦次级侧集电极引脚(④处),实测电压为0V,和③处电压相同。

4.测量R16阻值

R16上端(②处)电压为直流24V,而下端(③处)电压为直流0V,可大致说明R16开路损坏。断开空调器电源,待直流300V电压下降至直流0V时,如图6-43所示,使用万用表电阻挡测量R16阻值,正常值为4.7kΩ,实测阻值为无穷大,判断R16开路损坏。

图6-43 测量R16阻值

图6-43 测量R16阻值

5.更换R16 分压电阻

如图6-44所示,此机室外机主板通信电路分压电阻使用4.7kΩ/0.25W,在设计中由于此种功率设计偏小,容易出现阻值变大甚至开路故障,因此在更换时应选用加大功率、阻值相同的电阻,本例在更换时选用4.7kΩ/1W的电阻。

图6-44 更换R16电阻

图6-44 更换R16电阻

维修措施

如图6-45所示,更换分压电阻R16,参数为原4.7kΩ/0.25W,更换为4.7kΩ/1W。更换后,在空调器通上电源但不开机即处于待机状态时,测量室外机通信电路电压。

图6-45 测量室外机主板通信电路电压

图6-45 测量室外机主板通信电路电压

总结

本例由于分压电阻开路,通信信号不能送至室外机接收光耦,使得室外机CPU接收不到室内机CPU发送的通信信号,因此通过模块板上指示灯报故障代码为“通信故障”,并不向室内机CPU反馈通信信号;而室内机CPU因接收不到室外机CPU反馈的通信信号,2min后停止室外机的交流220V供电,并记忆故障代码为“通信故障”。

经验

判断4.7kΩ分压电阻是否开路的简单方法

①测量接线端子通信电压,待机状态下为直流24V,遥控开机,室内机主板向室外机供电后电压仍为直流24V不变,可说明室外机通信电路没有工作。

②测量4.7kΩ分压电阻上端电压为直流24V,下端电压为直流0V,两端压差在20V以上,即可判断分压电阻开路损坏。

③早期主板中4.7kΩ分压电阻容易阻值变大或开路损坏,主要原因是电阻功率选用0.25W相对较小,而通信电路中电流过大,如图6-46所示,后期主板已将4.7kΩ分压电阻功率改为1W。

图6-46 后期主板分压电阻功率改为1W

图6-46 后期主板分压电阻功率改为1W


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