With Manual A/C
CIRCUIT OPERATIONWhen the A/C Mode Selector Switch is in MAX, NORM, BI-LEVEL, or DEF, voltage is applied to the A/C Compressor Clutch through the A/C High Pressure Cut-Out Switch and the Pressure Cycling Switch.
The Pressure Cycling Switch turns the compressor off when the evaporator temperature is low enough to cause icing. It opens when the refrigerant pressure is less than 170 kPa (25 PSI). This opens the circuit to the A/C Compressor Clutch. This switch also closes to cycle the compressor on again when the evaporator temperature and pressure rise enough to require more cooling.
The A/C High Pressure Cut-Out switch will open if the pressure is above 2965 kPa (430 psi). This disengages the A/C compressor clutch and prevents the engine from overheating.
The Electronic Control Module (ECM) receives a voltage input signal when the A/C Compressor Clutch is engaged. The ECM turns on the engine cooling fans and increases the engine idle speed when the compressor is on.