Failure phenomenon
In a 2007 Jaguar S-TYPE car (equipped with automatic dual-zone air conditioning), the owner reported that the air outlet temperature on the right front side of the car could not be adjusted, and it was always warm, and the air outlet temperature on the left front side was adjusted normally.
Troubleshooting
Test drive after picking up the car, turn on the air conditioner, adjust the temperature on the left and right front sides to the coldest, blow cold air from the air outlet on the left front, and warm air from the air outlet on the right front; adjust the temperature on the left front and right front to the hottest , The left front side and the right front side air outlet both blow warm air, but the temperature of the air outlet on the right front side is higher than that of the air outlet on the left front side. Since the air outlet temperature on the left front side can be adjusted normally, it is suspected that the air distribution mechanism on the right front side is faulty or the signal of the air outlet temperature sensor on the right front side is wrong.
Detect with a fault detector, no fault code is stored in the air conditioning control module; read the signal of each outlet temperature sensor, no abnormality is found. Due to the lack of knowledge of the air distribution mechanism on the front right side of the car, in order to avoid blind disassembly and inspection, it was decided to check the maintenance information first. Looking at the maintenance data, we know that all the air from the blower first passes through the evaporator, and then part of the air is heated by the heater and then mixed with the remaining part of the air to obtain the air of the set temperature, and finally the air is blown out from the set air outlet. The heater consists of finned tubes that take heat from the engine coolant and transfer the heat to the air flowing through the heater. The heater is divided into two parts. The air flowing through one part is directly delivered to the left front side to adjust the air outlet temperature on the left front side, and the air flowing through the other part is directly delivered to the right front side to adjust the right front side air outlet. temperature. The air-conditioning control module adjusts the flow of engine coolant delivered to the two parts of the heater through dual coolant delivery valves to adjust the air temperature. The dual coolant delivery valve has 3 ports, one is the engine coolant inlet, and the other two are the engine coolant outlet, which provide engine coolant for the two parts of the heater.
Open the engine room cover, find the dual coolant delivery valve at the right front of the engine room (near the radiator), start the engine, turn on the air conditioner, adjust the temperature on the left front and right front to the coldest, touch the dual coolant delivery valve with your hand On the two outlet pipes, it is found that there is engine coolant flowing through one outlet pipe, and no engine coolant flows through the other outlet pipe; then adjust the temperature of the left front side and the right front side to the hottest Engine coolant flows through the two outlet pipes. Combined with the analysis of the failure phenomenon, it is inferred that the reason why the air outlet on the right front side always blows warm air is that the part of the heater responsible for heating the air on the right front side always has engine coolant flowing through. The possible causes of failure are: dual coolant delivery valve stuck; air conditioning control module failure; related circuit failure.
It can be seen from Figure 1 that there are two solenoid valves in the dual coolant delivery valve, one is used to control the flow of the engine coolant on the left front side, and the other is used to control the flow of the engine coolant on the right front side; the two solenoid valves share the power line, The working status is controlled by the air conditioning control module. Since the air outlet temperature on the left front side is adjusted normally, it indicates that the left front side solenoid valve is working normally, and the power supply of the dual coolant delivery valve is also normal. Use an oscilloscope to measure the control signals on the terminals FC40/27-05 and FC40/27-06 of the air conditioning control module at the same time, adjust the temperature on the left front side and the right front side to 22 ℃, and the measured control signal waveform is shown in Figure 2. . Comparing the control signals of the two solenoid valves, it can be seen that the air conditioning control module does not output a control signal to the right front solenoid valve. Since the signals of the air outlet temperature sensors are normal, it is inferred that the air conditioning control module is damaged.
Troubleshooting
After replacing the air conditioning control module, test drive, set the temperature, and adjust the temperature of the air outlet on the right front side to be normal. The fault is eliminated.
Fault summary
After troubleshooting, adjust the temperature of the left front side and the right front side to 22 ℃ again, and the measured control signal waveform of the dual coolant delivery valve is shown in Figure 3. Adjust the temperature of the left front side and the right front side to the coldest. The control signal waveform of the dual coolant delivery valve is shown in Figure 4; the temperature of the left front side and the right front side are adjusted to the hottest, and the control signal waveform of the dual coolant delivery valve is measured as shown in Figure 5.
Analysis of the above waveform shows that when the air conditioner temperature is set to the coldest, the air conditioner control module always provides a grounding signal to the solenoid valve in the dual coolant delivery valve, so that the dual coolant delivery valve is completely closed, preventing the engine coolant from entering the heater ; When the air conditioner temperature is set to the hottest, the air conditioner control module does not provide a grounding signal to the solenoid valve in the dual coolant delivery valve, so that the dual coolant delivery valve is fully opened, allowing the engine coolant to enter the heater at the maximum flow; When the air conditioner temperature is set to the temperature between the coldest and the hottest, the air conditioner control module provides a ground signal to the solenoid valve in the dual coolant delivery valve in the form of a duty cycle to control the opening of the dual coolant delivery valve. Degree to adjust the flow of engine coolant into the heater.