A/C Compressor Clutch Controls (3.0L)

NOTE: For A/C compressor clutch circuit testing, see appropriate MANUAL A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING. See appropriate SYSTEM WIRING DIAGRAMS article for terminal and wire color identification.

When A/C button on A/C-heater control panel is pressed, an A/C request signal is sent through the refrigerant pressure switch and Engine Control Module (ECM) to the coil of A/C compressor clutch relay (K60). The A/C compressor clutch relay is located at left front of engine compartment, in ECM housing. This enables A/C compressor clutch relay to energize, allowing ignition voltage to energize compressor clutch coil and fan control relay (K87).

When fan control relay energizes, battery voltage is supplied to auxiliary cooling fan No. 1, and through the normally open contacts of fan control relay (K52), to auxiliary cooling fan No. 2. If coolant temperature reaches 248°F (120°C), secondary temperature switch contacts will open and the compressor clutch coil is disengaged, causing A/C system to turn off. Secondary temperature switch will not allow A/C system to turn back on until coolant temperature has dropped to 239°F (115°C) or less.

Compressor clutch coil can also be turned off by refrigerant pressure switches (low pressure switch or high pressure switch). Low pressure switch will turn compressor clutch off as soon as refrigerant pressure falls to about 26 psi (1.8 kg/cm² ). This is done by opening the low pressure switch contacts and not allowing battery voltage to pass through A/C compressor clutch relay (K60) to compressor clutch coil. Low pressure switch activates the compressor clutch when refrigerant pressure increases to about 36.3 psi (2.6 kg/cm² ).

High pressure switch will turn compressor clutch off as soon as refrigerant pressure exceeds about 435 psi (30.6 kg/cm² ). This is done by opening the high pressure switch contacts in refrigerant pressure switch and not allowing battery voltage to pass through A/C compressor clutch relay (K60) to compressor clutch. High pressure switch activates compressor clutch when refrigerant pressure drops to less than about 290 psi (19.3 kg/cm² ).

When refrigerant pressure exceeds about 159.4 psi (11.2 kg/cm² ), A/C control switch contacts will close and engine idle speed will increase to compensate for RPM drop that occurs when A/C system is switched on. A/C control switch is installed in high pressure line, between A/C compressor and condenser. When refrigerant pressure drops to less than about 130.5 psi (9.2 kg/cm² ), A/C control switch contacts will close and allow engine idle speed to return to normal.