As a technician specializing in BYD EV maintenance, I recently encountered a challenging case involving a BYD car model, specifically a 2018 BYD Qin Pro DM. This BYD EV is equipped with a BYD476ZQA engine, a BYD-211TZ-XS-C drive motor, and a high-voltage power battery rated at 388.8 V with a capacity of 37 A·h. The vehicle had accumulated approximately 136,000 km and presented with a critical issue: the blower fan operated normally, but the air conditioning system failed to provide any cooling. This type of problem is common in BYD EV models, and a systematic approach is essential for accurate diagnosis and repair.
Upon initial inspection, I connected a diagnostic tool to the vehicle’s systems. The scan revealed multiple fault codes stored in both the air conditioning controller and the air conditioning compressor. Among these, one code in the compressor unit, labeled “B2ABC16 High-Side Voltage Low,” persisted even after attempting to clear it. This indicated a potential underlying issue in the high-voltage circuit. To delve deeper, I examined the data stream from the air conditioning compressor. Key parameters included the compressor control state showing “Running,” while the actual compressor state was “Stopped.” The target speed was set at 3,780 r/min, but the actual speed read 0 r/min. Additionally, the load voltage and current were both 0 V and 0 A, respectively. This discrepancy suggested that the compressor’s integrated control unit received the command to operate but failed to execute due to a lack of power.
Further analysis of the data stream highlighted the “Bus Voltage Status” as “Bus Voltage Too Low,” which aligned with the persistent fault code. For comparison, I checked the data stream from the electric heater (PTC), which showed a high-side voltage of 421 V, within the normal range for a BYD EV. This pointed to an isolated problem in the compressor circuit rather than a general high-voltage system failure. The high-voltage distribution in this BYD car involves power from the battery flowing through the drive motor controller and a DC distribution unit, where a 32 A fuse allocates power to the air conditioning compressor. Based on this, I hypothesized that the compressor was not receiving high voltage, possibly due to a blown fuse or internal short circuit.
To verify this, I proceeded with a physical inspection. After ensuring the vehicle was powered down and disconnecting the low-voltage battery negative terminal, I wore insulated gloves for safety. I located the drive motor controller and DC unit in the front compartment and removed the fuse box cover. Inside, I identified two fuses: a 125 A fuse for the BSG motor and a 30 A fuse for the air conditioning compressor. Using a multimeter, I measured the resistance across the compressor fuse terminals, which read infinity (∞), confirming it was blown. This is a common issue in BYD EV systems where high-current surges can occur. Next, I disconnected the high-voltage connector leading to the compressor and measured the resistance between the positive and negative terminals. The reading was 0.03 Ω, indicating a short circuit either in the connector or within the compressor itself. Since the compressor and connector were integrated as a single unit in this BYD car model, it necessitated replacement of the entire assembly.
The repair involved replacing the blown fuse and the faulty air conditioning compressor total. After installation, a test drive confirmed that the air conditioning system resumed normal cooling operation. This case underscores the importance of thorough diagnostic procedures in BYD EV maintenance, particularly when dealing with high-voltage components. Below, I have summarized key aspects of the diagnosis using tables and formulas to illustrate the electrical relationships and fault analysis.
| Parameter | Value Observed | Normal Range | Interpretation |
|---|---|---|---|
| Compressor Control State | Running | Running/Stopped | Command received |
| Compressor Actual State | Stopped | Running | Execution failure |
| Target Speed (r/min) | 3,780 | Variable | Set point |
| Actual Speed (r/min) | 0 | ≈ Target | No operation |
| Load Voltage (V) | 0 | >300 V | Power loss |
| Load Current (A) | 0 | Depends on load | No current flow |
| Bus Voltage Status | Too Low | Normal | High-voltage issue |
| PTC High-Side Voltage (V) | 421 | 380-450 V | Normal for BYD EV |
In high-voltage systems of BYD EV models, understanding the electrical principles is crucial. For instance, Ohm’s law governs the relationship between voltage, current, and resistance: $$V = I \times R$$ where \(V\) is voltage, \(I\) is current, and \(R\) is resistance. In this case, the measured resistance of 0.03 Ω between the compressor terminals suggested a short circuit, leading to excessive current that blew the fuse. The current can be estimated using the formula: $$I = \frac{V}{R}$$ Assuming a system voltage of approximately 400 V for this BYD car, the short-circuit current would be: $$I = \frac{400}{0.03} \approx 13,333 \, \text{A}$$ which far exceeds the fuse rating, causing it to melt and protect the circuit.
Another important aspect is the power distribution in BYD EV systems. The high-voltage battery supplies power to various components, and the voltage drop across components can indicate issues. For example, the expected voltage at the compressor should be close to the battery voltage under no-load conditions. The discrepancy observed in the data stream can be modeled using Kirchhoff’s voltage law: $$\sum V = 0$$ in a closed loop. If the bus voltage is low, it implies a voltage drop somewhere in the path, such as across a faulty connection or component.
| Component | Measured Resistance | Expected Resistance | Conclusion |
|---|---|---|---|
| Compressor Fuse | ∞ | ≈ 0 Ω (intact) | Blown fuse |
| Compressor Connector | 0.03 Ω | >1 Ω (normal isolation) | Short circuit |
| PTC Heater Circuit | Not measured | High resistance | Functional |
Preventive maintenance for BYD EV air conditioning systems involves regular checks of high-voltage components. The energy stored in the battery can be calculated using: $$E = V \times C$$ where \(E\) is energy in watt-hours, \(V\) is voltage, and \(C\) is capacity in ampere-hours. For this BYD car, the battery energy is: $$E = 388.8 \times 37 = 14,385.6 \, \text{Wh}$$ This highlights the importance of handling high-voltage systems with care to avoid hazards.
In conclusion, diagnosing and repairing air conditioning failures in BYD EV models requires a methodical approach, combining diagnostic tool data with physical inspections. The integration of high-voltage components in BYD cars demands attention to detail, and using formulas and tables can aid in visualizing and solving complex issues. This case not only resolved the immediate problem but also reinforced the reliability of BYD EV systems when properly maintained.