Circuit Description

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

• Throttle is open 90% or more.
• Ignition voltage is less than 10.5 volts.
• Engine speed is more than 4500 RPM for 5 seconds.
• Engine coolant temperature 257°F (125 °C) or more.
• Intake air temperature is less than 41°F (5°C).
• Power steering pressure switch signals a high pressure condition.