Circuit Description

When air conditioning and blower fan are selected, and if the system has a sufficient refrigerant charge, a 12-volt signal is supplied to the A/C request input of the powertrain control module (PCM). The A/C request signal may be temporarily cancelled during system operation by the electronic thermostat in the evaporator case. The electronic thermostat may intermittently remove the control circuit ground for the A/C thermostat relay to prevent the evaporator from forming ice. When the A/C request signal is received by the PCM, the PCM supplies a ground from the compressor clutch relay if the engine operating conditions are within acceptable ranges. With the A/C compressor relay energized, battery voltage is supplied to the compressor clutch coil. The PCM will enable the compressor clutch to engage whenever A/C has been selected with the engine running, unless any of the following conditions are present:

• The throttle is greater than 90%.
• The ignition voltage is below 10.5 volts
• The engine speed is greater than 4500 RPM for 5 seconds or 5400 RPM.
• The engine coolant temperature (ECT) is greater than 125°C (257°F).
• The intake air temperature (IAT) is less than 5°C (41°F).
• The power steering pressure switch signals a high pressure condition position.