1 Dongfeng Citroen C6L sedan for teaching produced in 2016, VIN number LDCC23661G1662S08. After starting the engine, turn on the blower switch, the air can be supplied normally, and then press the air conditioner P/C switch, no cold air is blown out from the air outlet.
2 Fault analysis and troubleshooting Firstly, connect the Diabox special diagnostic instrument to read the internal fault codes of the engine and air conditioning system modules. There are only some temporary fault codes. After deleting them, read them again and display no fault codes. Start the engine, through the "external environment" submenu in the engine diagnosis module, you can read the refrigerant pressure parameter as 10bar, as shown in Figure 1.
The engine electronic control unit ECU reads the refrigerant pressure information through the refrigerant pressure sensor, and transmits it to the intelligent control box BSI1 through the high-speed CPN communication network (communication rate S00kb/s), as shown in Figure 2.
It can be seen from the data parameters in Figure 1 that the refrigerant pressure is insufficient and the air-conditioning compressor is not working. Analyzed from Figure 2, the air-conditioning compressor is controlled by the engine compartment fuse box PSF1. The engine compartment fuse box PSF1 communicates with the intelligent control box BSI1 through the comfortable CPN network and accepts the control commands of the intelligent control box BSI1.
The engine electronic control unit ECU obtains the air-conditioning refrigerant pressure information and manages the cooling fan work, and transmits the "whether air-conditioning start information" to the intelligent control box BSI1 through the high-speed CPN network, and finally the intelligent control box BSI1 authorizes the engine compartment fuse box PSF1 Control the air conditioner compressor to work. The refrigerant pressure can reach 10bar, indicating that there is a certain amount of refrigerant in the pipeline, which can meet the starting demand of the air conditioner compressor.
After turning on the blower switch and the air conditioner P/C switch, it was found that the engine cooling fan was not working. It can be seen from the data sheet in Figure 1 that the fan relay has been activated. Turn off the engine, turn on the ignition switch to the ON position, and use the actuator test function of the diagnostic instrument to directly drive the fan. It was found that the fan was turning slightly-clothes, and quickly stopped.
The fan is driven in low-speed and high-speed working modes, and the working sound of the fan relay can be heard. In order to further rule out whether the fan motor works unstable, disconnect the fan relay to the fan motor wiring harness connector (Figure 3), and connect the test lamp.
I used the actuator test function of the clothing diagnostic instrument to drive, and found that in the high-speed drive mode, the test light was on-immediately after the clothing was turned off, similar to the fan rotation, indicating that the fan motor is not stuck, and the problem may be in the relay control. Check that the peripheral circuit of the fan relay is firmly connected and the fuse is normal. In order to confirm whether the performance of the fan relay is good, the fan relay on another C6L car with a normal cooling fan is removed and replaced.
Driven by the actuator test function of the diagnostic instrument, the fan can rotate normally at low speed and high speed. Start the engine, turn on the blower speed control switch, press the air conditioner P/C switch, you can hear the sound of the air conditioner compressor, and the air outlet can blow cool breeze. Read the refrigerant pressure parameter to reach 16bar, see Figure 6.
3 Fault summary The dry engine cooling fan is not working properly, and the engine electronic control unit ECU cannot receive the feedback signal that the fan continues to work, so it transmits the information to the intelligent control box BSI1 to control the engine compartment fuse box PSF1 to cut off the air conditioning compressor. . After replacing the fan relay, troubleshooting.