【Fault description】
    Because the air conditioning is not cooling into the factory maintenance, after filling the refrigerant. The compressor still does not pull.
    【Inspection process】
    Run the engine, press the air conditioner panel air conditioner switch, cooler rear cooling fan and condenser fan can be run. Only the compressor does not pull. Find the compressor electromagnetic clutch relay, shorted 30 and 87 terminals, the clutch can pull in: the relay seat on the 85 and 86 terminals in series with a test light to check that the direct cause of the fault is the engine control unit The ECU does not execute the pull command. In order to verify that the air conditioning switch signal has reached the ECU. In the former passenger foot plate to find the ECU control unit, found that the pin with our existing circuit map data does not match. But with a car system, should have the same control characteristics.
    【Fault Analysis】
    It can be seen from the circuit diagram, air-conditioning air-conditioning switch to be used to help the heating fan switch, that is, only the heating fan operation, air conditioning air-conditioning switch to work, and then the grounding signal through the thermostat switch, air conditioning pressure switch to ECU, ECU This "air conditioning request signal", it is possible to trigger the electromagnetic clutch relay pull. At the same time, the closure of the air-conditioning switch will make the two cooling fan relay control side of the line through a diode after the ground, so that the fan synchronous operation. According to this idea, we found this "air conditioning request signal" line by measuring. Press the air conditioner switch between 12V and OV. Next, measure the electromagnetic clutch relay control circuit of the ECU, which is connected to the terminals of the relay. At this point, the fault has nothing to do with the external lines of the air conditioning system.
    We know that the engine ECU control of the compressor clutch is conditional, such as the throttle angle open rate, the engine temperature, etc., where the water temperature signal is one of the factors, through the test and the necessary measurement work, that the engine water temperature The sensor signal is in the normal voltage range r8. The engine system self-diagnosis also has no fault code output. Comprehensive analysis, failure should be in the ECU itself, replace the new pieces. The fault is completely eliminated.
    【Maintenance】
    In the maintenance found that Honda this problem more. Some owners feel the cost of replacing the ECU is expensive, so we will ECU pin "air conditioning request signal" line and electromagnetic clutch control line together, after 3 months of tracking feedback. The system works well. In addition, the circuit according to the characteristics of circuit control, this connection method will not cause damage to the ECU, and because the external circuit with a series of diodes, and fan control lines will not interact, so it is a more economical solution.