According to your description, there are two reasons for this situation: first, it may be due to the failure of your back line; On the other hand, because your back switch or air switch trips or fails, it is recommended that you check whether the back switch trips first. If so, please reset the reversing switch under the condition of ensuring your own safety. If it is impossible to judge, it is recommended that you entrust qualified construction personnel to check and deal with it.
I hope our answer is helpful to you. If you have any other questions, please feel free to call the 24-hour service hotline of power supply customer service for consultation.