A/C Compressor Clutch Controls

NOTE: For A/C clutch testing, see CIRCUIT DIAGNOSIS TESTS or the A/C COMPRESSOR CLUTCH CONTROLS article in the AIR CONDITIONING & HEAT section. See appropriate diagram in WIRING DIAGRAMS article for terminal/wire color ID. For component locations, see COMPONENT LOCATION .

When A/C button on A/C-heater control panel is pressed, an A/C compressor request signal is sent through the refrigerant pressure switch and the Engine Control Module (ECM) to the coil of the A/C compressor relay (K60). Relay is located at left front of engine compartment, in ECM housing. This enables A/C compressor relay to energize, allowing ignition voltage to energize A/C 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), temperature switch No. 2 contacts will open and the compressor clutch coil is disengaged, causing A/C system to turn off. Temperature switch No. 2 will not allow A/C system to turn back on until coolant temperature has dropped to 239°F (115°C) or less.

A/C compressor clutch coil can also be turned off by refrigerant pressure switches (low pressure switch or high pressure switch). Low pressure switch will turn A/C 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 relay (K60) to compressor clutch coil. Low pressure switch activates the A/C compressor clutch when refrigerant pressure increases to about 36.3 psi (2.6 kg/cm² ).

High pressure switch will turn A/C 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 relay (K60) to A/C compressor clutch. High pressure switch activates A/C compressor clutch when refrigerant pressure drops below 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 below about 130. 5 psi (9.2 kg/cm² ), A/C control switch contacts will close and allow engine idle speed to return to normal.