BYD Han EV Insufficient A/C Cooling: Complete Diagnosis from Compressor to Backed-Out Wiring Terminal

Fault Background

The Han EV uses a heat pump air conditioning system, consisting of an electric scroll compressor, electronic expansion valve (EXV), and integrated thermal management module. Compared to the traditional fuel vehicle configuration of "belt-driven compressor + mechanical expansion valve," the additional actuators and control logic in the refrigerant circuit of new energy vehicles make the troubleshooting path for "A/C not cold enough" completely different. This article fully reconstructs the diagnostic and repair process through a real case.

Fault Symptom

Cause Analysis

1. Electric compressor fault – Internal wear or control abnormality in the compressor can reduce cooling capacity and cause abnormal noise; it is the first suspect.
2. Electronic expansion valve (EXV) malfunction – When the EXV opening is insufficient, refrigerant circulation is obstructed, causing the low-side pressure to rise abnormally, and the controller may not set a DTC.
3. Wiring and connector faults – Backed-out terminal pins or poor contact in connectors can prevent the controller's commands from being "sent out and executed properly." Such faults often have no DTC and are the hardest to detect.

Diagnostic Procedure

1. Read DTCs and live data stream: First confirm whether the controller has recorded any faults, and read key data such as actual compressor speed and power.
2. Check refrigerant pressure: Connect a manifold gauge set to confirm high- and low-side pressures, and determine whether the issue is refrigerant quantity or circuit blockage.
3. Inspect the electric compressor: Listen for abnormal operation noise; after replacing the compressor, if the noise disappears but cooling remains insufficient, the compressor is a "result" rather than the root cause.
4. Read compressor live data: Actual speed 7029 r/min, power 3803 W – both speed and power are simultaneously high, indicating the system is "compressing hard," suggesting downstream circuit obstruction.
5. EXV actuator function test: Use the diagnostic scan tool to force a set opening (e.g., 30%), and touch the valve body to confirm whether it actuates. The evaporator-side EXV shows vibration response, while the plate heat exchanger-side EXV shows no response – the fault direction is confirmed.
6. Measure EXV coil resistance: Measured at approximately 50 Ω, which is within the normal range. The valve itself is not faulty; the issue points to power supply and wiring.
7. Inspect wiring harness connectors: Check each pin of the front compartment harness connector to the plate heat exchanger-side EXV; one pin is found backed out. After re-securing the terminal, a test drive confirms cooling is restored.

Repair Plan

1. Replace the faulty electric compressor (source of abnormal noise) to restore compressor efficiency.
2. Repair the backed-out terminal pin in the front compartment harness connector: remove the terminal, correct the locking tab, re-insert it fully, and perform a pull-back test.
3. After reassembly, perform an EXV actuator function test to confirm proper response, and recover/recharge refrigerant to the standard amount.
4. Road test and re-measure vent outlet temperature and high/low-side pressures to confirm cooling performance is restored.

Key Parameter Quick Reference

Safety Warnings

• Before servicing the heat pump/A/C system, the vehicle must be powered down. Work on high-voltage components requires certification and must follow the OEM "power off first, then verify voltage" procedure.
• Refrigerant recovery and charging must use dedicated equipment; direct release is prohibited.
• The electronic expansion valve is a precision actuator; do not forcibly turn the valve stem during function tests.

Repair Insights

"A/C not cold enough" is most easily misled by habitual thinking: refrigerant leak, expansion valve blockage, and compressor failure are almost the only answers from the fuel vehicle era. However, new energy vehicles have electronic actuators and bus control. The three-step approach of live data + actuator function test + terminal inspection is essential to catch the true fault chain of "high speed and power, no EXV response, and backed-out terminal pin." Replacing the compressor solved the noise but not the cooling – the lesson is: Before replacing any part, prove it is the root cause, not the consequence.

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【This article is for reference only】