Manual Climate Controls

DESCRIPTION

The compressor for the air conditioning system is belt-driven by the engine through the A/C compressor clutch. The clutch allows the compressor to cycle on and off during normal operation, disengage when air conditioning is not requested, or disengage when engine load must be reduced. The A/C compressor is not activated if the ambient temperature is below 7.2-10 °C (45-50 °F).

OPERATION

With the heater and A/C control mode selector knob in MAX A/C, NORM A/C, BI-LEVEL, DEFOG or DEFROST, the A/C high-pressure cut out switch closed and the pressure cycling switch closed, battery voltage is applied to the powertrain control module (PCM). This voltage signal tells the PCM that A/C compressor operation is requested.

Under normal operating conditions, the PCM then grounds the A/C compressor control relay coil, and the relay energizes. Voltage is applied to the A/C Compressor clutch through relay center fuse 5 and the A/C compressor control relay contracts. The A/C compressor clutch engages and the compressor runs.

The compressor runs until A/C system low-side pressure drops to the point where the pressure cycling - switch contacts open, 152 kPa (22 psi). When the contacts open, the voltage signal to the PCM is interrupted and the PCM de-energizes the A/C Compressor control relay. The A/C compressor clutch disengages and the compressor stops running. When A/C system low-side pressure rises to about 296 kPa (43 psi), the pressure cycling switch contacts close again and the compressor begins running.

The A/C high-pressure cut-out switch contacts are normally closed. If A/C system high-side pressure rises too high, the switch contacts open interrupting the voltage signal to the PCM. The PCM then de-energizes the A/C compressor control relay and the compressor stops running.

If the PCM determines that engine load should be reduced, such as during full throttle conditions, it will de-energize the A/C compressor control relay to disengage the compressor, even through the voltage signal from the heater and A/C control is still present.

The A/C compressor clutch diode, connected across the terminals of the A/C compressor clutch, provides a path for the current resulting from voltage spikes. The voltage spikes are generated by the collapsing magnetic field of the A/C compressor clutch coil and one occurs every time the coil is de-energized.