Trouble phenomenon:

The air-conditioning system does not work, and there is no response when pressing any button on the air-conditioning control panel.

Analyze the reasons:

1. Air-conditioning system fuse blown
2. Line fault
3. Engine computer failure
4. Air conditioning control unit failure
5. Air conditioning sensor and actuator failure

Diagnosis process:

Circuit diagram analysis
From simple to complex, first, confirm the status of the fuse.Confirm the working status of each related fuse: normal.


  1. According to the terminal of the air conditioner control unit connector, confirm whether there is a power supply at the power end:
  2. Power terminal A9 inspection result: normal
  3. Further, check the ground terminal:
  4. Both the B3 ground terminal and the B5 power transistor control ground terminal work normally.
  5. Use HDS to connect to the vehicle and try to connect to the air conditioning control unit, but found that the air conditioning unit cannot be connected to the HDS. Therefore, it is judged that there is a problem with the output of the air conditioning unit.
  6. Use the air conditioner self-diagnosis to obtain the fault codes: L and A/C, refer to the list of fault codes: the inner loop control motor circuit is short-circuited.
  7. After unplugging the inner loop control motor connector, the air conditioning system resumes work. The HDS can be used to connect the air conditioning control unit normally.

Analysis of the cause of the failure

  1. Disassemble and inspect the internal circulation control motor actuator of the air conditioner, and found that its connecting rod is stuck.
  2. The output voltage of the Biz terminal of the measurement control unit is less than 5V.
  3. It is inferred that the cause of the fault is that the inner loop control motor connecting rod is stuck and cannot be rotated, causing the line to be damaged and short-circuited, and the control unit outputs

The output voltage is less than 5V, unable to respond to key operations, and eventually, cause the air conditioning system to not work.
Troubleshooting: Replace the inner loop control motor actuator, and eliminate the fault.
Experience summary: All control units on Honda vehicles work with a 5V power supply. There is a 12V/5V converter inside, which has low power. If its load is short-circuited or consumes too much power, it will cause the operating voltage of the internal processing unit to drop. Or it can't work normally, but it will not cause a short circuit of external power supply circuit ((12V)) or overload insurance.
This is also a characteristic of this example, and it is worthy of attention by maintenance personnel in their daily work.

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