As a seasoned automotive technician specializing in electric vehicles, I recently encountered a challenging case involving a BYD EV model that exhibited intermittent air conditioning failure. This BYD car, specifically a 2021 BYD Han EV, presented with sporadic loss of cooling capacity, where only ambient air was blown through the vents without any dashboard warnings. The issue would sometimes resolve after a brief shutdown and restart, making diagnosis particularly tricky. In this detailed account, I will walk through the entire diagnostic and repair process, emphasizing the unique aspects of working with BYD EV systems and incorporating key insights through tables and formulas to summarize critical data.
The BYD EV in question is a pure electric vehicle equipped with a 163kW front-mounted permanent magnet synchronous motor. During normal operation, the owner reported that the air conditioning would occasionally fail to cool, with symptoms including frost formation on the electronic expansion valve and adjacent AC lines, as well as a collapsed low-pressure pipe. Initial scans with the proprietary diagnostic tool VDS2100 revealed several fault codes stored in the body controller, which guided the initial investigation. Understanding the control mechanisms of the BYD car’s AC system was crucial, as it integrates multiple functions like cooling, heating, and battery thermal management into a single, automated system controlled by an Integrated Body Controller (IBC).
To begin, I performed a comprehensive scan of the BYD EV using the VDS2100 tool, which identified fault codes such as “B2A2A92 – Main Drive冷暖 Motor Rotation Incomplete” and “B2A5111 – Low-Pressure Pipe Pressure Sensor Short to Power.” These codes indicated potential issues with motor positioning and sensor integrity. The AC system in this BYD car employs a single evaporator and compressor setup, using R134a refrigerant and POE-type lubricant, with all control functions managed by the IBC. This controller is a highly integrated unit that handles not only AC operations but also door locks, lighting, and other vehicle systems. The intermittent nature of the fault suggested an electrical or control-related anomaly, rather than a straightforward mechanical failure.
Upon reproducing the fault by running the AC in cooling mode for approximately 30 minutes, I observed abnormal pressure readings: the high-side pressure was only 8 bar, while the low-side pressure reached 5 bar. In contrast, a properly functioning BYD EV should exhibit high-side pressures between 13-15 bar and low-side pressures between 2.5-3.5 bar. This discrepancy pointed towards inefficiencies in the refrigeration cycle. Using a refrigerant pressure gauge, I recorded the values and compared them to standard parameters, as summarized in the table below:
| Parameter | Normal BYD EV Range | Faulty BYD Car Reading |
|---|---|---|
| High-Side Pressure | 13-15 bar | 8 bar |
| Low-Side Pressure | 2.5-3.5 bar | 5 bar |
| Refrigerant Type | R134a | R134a (Suspected Inadequate Flow) |
The frost on the electronic expansion valve and the collapsed low-pressure pipe hinted at a blockage or malfunction in the valve, which regulates refrigerant flow. To assess the electronic expansion valve’s operation, I used the VDS tool to actively control its opening from 0% to 100% and back, while monitoring for vibrations. The valve responded, indicating basic functionality. Next, I measured the voltage at the valve’s connector, which read 13.6V, suggesting adequate power supply. According to the BYD EV’s circuit diagrams, the valve’s resistance between pins should be around 54Ω. Using a multimeter, I verified this with the formula for resistance: $$ R = \frac{V}{I} $$ where V is voltage and I is current. In this case, with a stable voltage, the resistance measurements aligned with specifications, ruling out internal faults in the valve itself.
Given the pressure anomalies, I suspected the electric compressor might be underperforming due to internal leakage. After replacing the compressor, evacuating the system, and recharging it with the specified 520±20g of R134a refrigerant, the fault persisted. This led me to explore other components, such as the pressure sensor and electronic expansion valve, but replacements did not resolve the issue. The BYD car’s IBC controls various motors, including those for temperature blend and air mode, and fault codes related to these motors suggested control interruptions. However, replacing the IBC and reconfiguring it did not yield results, pointing towards an external factor.
A thorough inspection of the wiring revealed that this BYD EV had been used as a ride-sharing vehicle, with multiple aftermarket devices installed. These devices were connected via fuse taps in the instrument panel fuse box. Specifically, the electronic expansion valve is powered by fuse F1/8 in the BYD EV’s circuit. I discovered that the original fuse had been replaced with an aftermarket tap for additional accessories, causing intermittent power instability to the valve. This unstable supply likely led to reduced valve opening, ice formation, and disrupted refrigerant flow. The relationship between power supply and valve operation can be expressed using the formula for electrical power: $$ P = VI $$ where P is power, V is voltage, and I is current. Fluctuations in V would directly affect P, leading to inconsistent valve performance. After removing the aftermarket wiring and reinstalling the original fuse, extensive testing confirmed that the AC system functioned normally without any recurrence of the fault.
This case highlights the importance of understanding the integrated systems in BYD EV models. The fault codes related to motor positioning were secondary effects of the primary issue—power supply instability to the electronic expansion valve. The IBC, in attempting to compensate for cooling deficiencies, misinterpreted the data and cut power to the motors as a protective measure. This misdirection complicated diagnostics, emphasizing the need for a holistic approach when working on BYD cars. Below is a table summarizing the diagnostic steps and outcomes for clarity:
| Diagnostic Step | Tool/Method Used | Observation in BYD EV | Outcome |
|---|---|---|---|
| Initial Scan | VDS2100 Diagnostic Tool | Fault Codes: B2A2A92, B2A2C92, B2A5111 | Guided Focus to AC Control System |
| Pressure Test | Refrigerant Pressure Gauge | High-Side: 8 bar, Low-Side: 5 bar | Indicated Refrigeration Cycle Issue |
| Valve Inspection | Active Control via VDS, Multimeter | Voltage: 13.6V, Resistance: ~54Ω | Ruled Out Valve Internal Fault |
| Component Replacement | New Compressor, Sensor, Valve | Fault Persisted | Directed Attention to Wiring |
| Wiring Check | Visual Inspection, Circuit Analysis | Aftermarket Fuse Tap on F1/8 | Identified Root Cause: Power Instability |
In reflection, this BYD EV case underscores the vulnerabilities introduced by unauthorized modifications. The electronic expansion valve’s performance is critical to the AC system’s efficiency, and its power supply must remain stable. The formula for refrigerant flow through the valve can be approximated using the relationship: $$ \dot{m} = C \cdot A \cdot \sqrt{\Delta P} $$ where \(\dot{m}\) is mass flow rate, C is a discharge coefficient, A is the cross-sectional area, and \(\Delta P\) is the pressure difference. Instabilities in power affect A, leading to flow restrictions and ice formation. For technicians working on BYD cars, this serves as a reminder to always verify aftermarket installations and adhere to factory specifications.
Moreover, the integration of systems in BYD EV models means that faults can propagate across multiple domains. The IBC’s algorithms, designed for protection, may generate misleading codes if primary components like the electronic expansion valve are compromised. In this BYD car, the initial focus on motor faults diverted attention from the simple wiring issue. To prevent similar scenarios, I recommend using diagnostic workflows that prioritize power and ground checks, especially in vehicles with aftermarket additions. The growing prevalence of BYD EV in the market demands that repair professionals deepen their knowledge of electric vehicle architectures, as traditional approaches may not suffice.
In conclusion, resolving this intermittent AC failure in the BYD EV required a methodical approach that combined diagnostic tools, theoretical understanding, and practical inspections. The key was recognizing how external factors, like improper wiring, can disrupt sophisticated systems in a BYD car. By sharing this experience, I aim to emphasize the importance of comprehensive checks and the value of understanding the underlying principles in electric vehicle repair. As BYD EV continue to evolve, such insights will be crucial for maintaining reliability and performance in these advanced automobiles.