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When the vehicle is in use, the engine generates excessive heat. In order to make the engine not work properly due to overheating, a cooling liquid circulation cooling system is designed, in which the cooling fan plays a pivotal role. For the electronically controlled cooling fan, the control methods used by different models are different. The following is a combination of two fault examples to understand the working principle and troubleshooting of the two common electronic fan control methods.
Example 1 A car with a displacement of V62.4L, the cooling system of the car is "opened" because the electronic fan does not turn, and the electronic fan still cannot run when the air conditioner is turned on. The control of the radiator fan of this Audi car is realized by controlling the ground wire of the fan relay through the dual temperature thermal switch. There are two electronic fans in the cooling fan system of the car. The red wire in their connection harness is the positive wire, the brown wire is the ground wire (directly fixed on the beam), and the red positive wire is a positive wire on the right beam. fixed at the column.
The control of the red positive line is divided into fan low-speed relay, air-conditioning relay and fan high-speed relay control. Pay attention to their specific positions during maintenance. The fan low-speed relay is located in the third relay position in the fuse box on the right side of the engine, and the fan high-speed relay is installed in the No. 217 relay in the auxiliary fuse box under the driver's feet. The low and high speed of the fan The operation is realized by the dual temperature thermal switch on the radiator, which controls the grounding of the relay according to the temperature of the coolant.
When the air conditioner switch is turned on, the fan low speed relay is controlled by the air conditioner fan relay to make the cooling fan rotate. The ground wire (green/yellow wire) of the No. 217 relay is connected to the dual temperature thermal switch. Once the coolant temperature rises to a certain temperature, the dual temperature thermal switch controls the relay to ground, and the cooling fan will enter a high-speed operation state. In addition, the main live wire and control live wire of No. 217 relay are all broken when the ignition switch is turned on?
According to the working principle of the cooling fan system of the car, it is found that the car lacks a fan low-speed relay (the user reported that the car has been repaired in other repair shops). But after it is installed, the cooling fan has only high-speed gear and no low-speed gear. After careful inspection, it was found that the No. 217 relay was burned, causing the cooling fan to always run at a high speed. After the No. 217 relay was replaced, the fault disappeared. Example 2 In a Samsung Jielong car, the water temperature gauge shows normal temperature during driving, but if the engine is stopped and the engine is running at idle speed, although the water temperature gauge shows between 90-100 degree , the cooling system has been "opened" at this time. At this time, it was found that the cooling fan could not operate at all. The control method of the cooling fan of this car is very different from that of the Audi car. This Samsung Jielong car cooling fan is controlled by the car computer. After inspection, the cooling fan relay lacks the control ground wire. When the engine is running at idle speed, the actual temperature of the coolant is measured with a thermometer and has reached 110 degree , but the water temperature gauge of the car still indicates between 90-100 degree . Using a multimeter to measure the resistance of the water temperature sensing plug is about 100 ohms. Therefore, it is initially suspected that the water temperature sensing plug is damaged.
In the absence of replacement parts, find a 2k ohm sliding variable resistor in parallel with the water temperature sensing plug to reduce the resistance value. If the sliding variable resistor is adjusted at this time so that the temperature displayed by the water temperature gauge is consistent with the actual temperature of the coolant, the cooling fan actually operates normally with the increase in temperature.
It appears that the cause of the malfunction is the water temperature sensor plug. Because the water temperature sensing plug is damaged, it always gives the car computer a low temperature error signal that the cooling fan cannot be operated. Naturally, the cooling fan cannot operate normally. Finally, after replacing the water temperature sensing plug, the car returned to normal.
It can be seen that the computer of this car receives the input signal of the water temperature sensor plug, and when the water temperature reaches the specified value, the computer controls the ground wire of the fan relay to ground to make the cooling fan run. The above are two completely different control methods, but as long as we figure out their working principle and conduct careful inspection and analysis of the fault, the problem in this area can also be quickly solved.
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