Air conditioning compressor clutch control
Note. Refer to illustrations 6.2a and 6.2b c to determine relay installation locations section 6 chapter 12.
44. During the operation of the air conditioning system, the system compressor clutch is switched on and off by commands from the ECM / PCM. The ECM/PCM controls the operation of the air conditioning compressor clutch relay, delaying clutch engagement for approximately 8 seconds (on engines 3.1 l) or 0.4 seconds (on 3.8 l engines) after turning on the A/C system: this allows the IAC valve to adjust the idle speed to accommodate the extra load. In addition, the ECM/PCM uses the same relay to disengage the clutch during full throttle engine operation to avoid excessive compressor speed.
45. The attached diagnostic diagram shows the sequence of operations for checking the control of the compressor clutch (see illustration).
4.45a. Use a test light to check if the pink/white wire going to the air conditioning control relay electrical connector is 12 volts
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4.45b. Sequence diagram for checking the air conditioning clutch control mechanism
Signal "Turn on air conditioning" (pressing a button in the cabin)
46. When a signal is given to turn on the air conditioning system, the voltage from the battery is supplied to the compressor clutch and to the terminal "AT 8" (on 3.1 l engine) or "BD11" (on 3.8 l engine) ECM/PCM electrical connector through circuit "67" (blue wire going to the pressure switch) (see illustration 4.45c), resulting in an increase in air consumption at idle, which ensures that the desired idle speed is maintained.
47. In most cases, the cause of the failure of the air conditioning system is not the ECM / PCM, but the control relay and switches of this system.
48. If the air conditioning system is operating normally, but the idle speed when the system compressor is turned on is very low or, conversely, too high when it is turned off, check for open circuits in the circuit section (dark green with white wire) between A/C control relay and ECM/PCM to ECM/PCM (see illustration 4.45v or 4.45g). If this section of the circuit is not damaged, the fault should be sought in the contact "AT 8" (for 3.1L engine), "BD11" (for 3.8L engine) the ECM/PCM or in the ECM/PCM itself.
4.45v. Scheme of the section of the electrical circuit with the control relay of the air conditioning system of cars with a 3.1 liter engine
4.45g. Scheme of the section of the electrical circuit with the control relay of the air conditioning system of cars with a 3.8 liter engine