Fault Symptoms:
A 2017 Honda Accord equipped with a 2.0L engine and a CF8A CVT transmission, with a mileage of 100,000 km, underwent accident repairs. Repairs included replacing the front bumper and accessories, two front headlights and brackets, the engine hood and hinges, and the front windshield, as well as restoring both front fenders and left and right longitudinal beams. After refilling the A/C refrigerant (R-134a), the A/C system stopped functioning.
Inspection and Analysis:
The repair team vacuumed the A/C system and, using an A/C pressure gauge, attempted to add liquid R-134a by inverting the refrigerant can and opening the high-pressure valve with the vehicle off. When the refrigerant did not enter the system, they closed the high-pressure valve, opened the low-pressure valve, started the engine, and activated the A/C, but the pressure gauge showed no change.
Upon further inspection, it was found that the A/C compressor clutch was not engaging, and neither the radiator fan nor the condenser fan was operational. No warning lights were displayed on the dashboard. Normally, the A/C compressor clutch, radiator fan, and condenser fan would activate simultaneously. These symptoms pointed to potential issues with the A/C pressure sensor or evaporator temperature sensor circuits.
The A/C pressure sensor, located on the receiver-drier at the condenser outlet, adjusts output voltage according to pressure changes. The Powertrain Control Module (PCM) uses this signal to operate the compressor and control the radiator and condenser fans. If system pressure exceeds 2,850 kPa or drops below 196 kPa, the PCM disables the compressor for protection.
The evaporator temperature sensor, a chip-based thermistor, is mounted on the evaporator fins to monitor temperature. If the temperature approaches freezing, the compressor and fans momentarily stop to prevent frost accumulation, which can reduce airflow and A/C efficiency.
Using the HDS diagnostic tool, the team identified fault code “P0533 – A/C Pressure Sensor Circuit Voltage High” in the fuel emissions system. While running the engine at idle with the blower and A/C switches on, the pressure sensor’s data stream showed a voltage of 5.00V, exceeding the normal range of less than 4.75V. This suggested possible causes: a faulty pressure sensor, damaged wiring between the sensor and the HVAC control unit, or an HVAC control unit malfunction.
Removing the front bumper revealed a broken blue wire in the pressure sensor harness caused by the accident. The wire, connected to the PCM’s A10 ground terminal, caused the sensor’s voltage to read abnormally high.
Troubleshooting:
The broken blue wire was repaired and insulated with tape, and the sensor harness was wrapped for protection. After restarting the engine and activating the A/C, the pressure sensor voltage read 1.04V, which is within normal limits. The compressor clutch engaged, and both the condenser and radiator fans operated correctly. The refrigerant was refilled to standard levels, all fault codes were cleared, and a performance test confirmed the system functioned properly. After reassembling the bumper, a final road test verified the issue was resolved.
Summary:
This Honda Accord features a manual A/C system where fault codes are accessible via the fuel emissions system. By analyzing A/C-related data streams from the emissions system, the diagnostic process was streamlined to efficiently identify and resolve the issue.
