A/C Switch
WARNING: This page is about a different car, the 2002 Mercury Villager. However, it is still accessible from the selected car via links, so may be relevant.
When ambient temperature is more than 48°F (9°C), turning A/C switch on completes compressor circuit. Powertrain Control Module (PCM) energizes compressor (magnetic) A/C clutch relay, which engages compressor clutch.