Compressor Control

A/C Compressor Clutch
With the engine running, battery voltage from fuse 8 is applied to the A/C switch and the A/C dual pressure switch. When the A/C switch is switched ON, voltage is applied to the coil of the A/C thermostat relay. Ground is provided to the coil of the relay through the electronic thermostat and the blower switch (provided the blower switch is not in the OFF position). The A/C dual thermostat really energizes and voltage is applied through the A/C pressure switch and the closed contacts at the A/C thermostat relay to the A/C compressor clutch and the fast idle solenoid valve. The A/C compressor clutch engages and the fast idle solenoid valve increase the engine idle adjustment to keep engine speed constant while the A/C is ON. If the A/C dual pressure switch opens. the A/C compressor disengages.

A/C Dual Pressure Switch
A/C system pressure below 196 20kPa (28 3 psi) indicates a loss of refrigerant or refrigerant oil. The A/C pressure switch opens with low system pressure to prevent compressor damage. Also, with system pressure above 2648 ± 196 kPa (384 ± 28 psi), the A/C pressure switch opens to prevent compressor damage.

Electronic Thermostat
The electronic thermostat senses the temperature of the cool air from the evaporator and the evaporator fins by means of the evaporator temperature sensor. This information is input by the electronic thermostat, which determines whether ground is to be provided to the A/C thermostat relay. When the temperature becomes too low, ground is not provided.