Why BMW X5 air conditioning is not working properly

Failure phenomenon: a 2003 annual BMW E53 X5 SUV, equipped with M62 engine. According to users complained that the car’s air conditioning is set to warm, about half an hour still no warm air outlet, this failure is not often.

inspection and analysis: First, after the car is idling, turn on the air heater is working properly, 20 min after the failure phenomenon did not occur. BMW special connection fault diagnostic GT1, see the air conditioning system does not malfunction information storage, read data stream also found no problems.

Main components of the car is equipped with an automatic climate control system (IHKA), let’s briefly understand the following air-conditioning system.


(1) interior temperature sensor (FIG. 1): a sensor for forced ventilation with forced draft fan (FIG. 2), mounted in the air conditioning control panel, the temperature of the air measured by the sensor by the forced draft fan integrated in the suction cabin.

FIG. 2

(2) Light sensor: in the middle of the instrument panel is mounted, outside the presence of the probe may affect the temperature inside the car or light a heat source (e.g., sunlight), this sensor is only activated in the air conditioner automatic mode.

(3) vehicle automatic cycle control sensors: upper collector hood mounted on the measuring side of the fan downwash, HC recognition engine, CO, and NOx emissions of harmful substances.

(4) mist sensor: to measure the air inside the vehicle cabin inner side of the windshield and a relative humidity of the air conditioner automatic mode, automatic identification mist may condense to mist before it windscreen.

(5) a refrigerant pressure sensor: high-pressure pipe is mounted in the path between the condenser and the evaporator. When the system pressure is too high, the air conditioner control unit turns off the compressor based on the sensor signal.

(6) air-conditioning system control unit: the air conditioner operating panel composed of a member.

Through the above description, we have air conditioning for the carWith a simple understanding of the system, the next overhaul failure. Start the engine, and opens the hot air temperature was set at 20 ℃, about 20 min after start blowing outlet natural wind. Read the data stream, the interior temperature sensor measurement display 20 ℃, but feel the value higher than the actual temperature of the vehicle. Remove the air conditioning control panel, the forced draft fan observed vehicle temperature sensor does not turn, hand tapping the fan, the fan starts to rotate, and the outlet hot air is blown at this time, it seems to find the point of failure.

Troubleshooting: since the forced draft fan can be replaced individually, then the control unit can replace the air conditioning assembly (FIG. 3). After the replacement, air conditioning back to work.

Figure 3

reviewed: Since vehicle temperature control is achieved by the air conditioning system to achieve a control unit, which controls the occupant is provided standard values ​​measured on the temperature sensor and the target vehicle interior temperature actual temperature based on the value, the adjustment is the difference between the two. Therefore, when the forced draft fan is not running, the temperature value measured by the interior temperature sensor is not the actual temperature of the cockpit, but the temperature inside the control panel. Internal control panel has many electronic components, gives off a lot of heat during operation, which leads to the interior of the control panel the temperature higher than the actual temperature in the vehicle cabin, the air conditioning system in accordance with this time control unit controls the interior temperature sensor signal, cause no blow warm air outlet.

(Zhang Sheng)

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