1. The Clutch Itself:
* Visual Inspection: Look for obvious damage like broken wires, a seized bearing, or a bent pulley. The pulley should spin freely when the clutch is *disengaged*.
* Continuity Test: With the ignition ON, use a multimeter to check for continuity across the terminals of the clutch. You should have continuity if the clutch is supposed to be engaged (AC turned on). Lack of continuity might indicate a bad clutch coil.
2. The Compressor:
* Check for Leaks: Inspect the compressor for any signs of refrigerant leaks (oil stains, hissing sounds). A low refrigerant charge will prevent the clutch from engaging, even if everything else is working. *This requires specialized equipment.*
* Listen for Noise: If the compressor is seized, it will make grinding or squealing noises.
3. The AC System Pressure:
* *This requires specialized equipment.* Low refrigerant pressure will prevent the clutch from engaging to protect the compressor. A qualified technician needs to check this with gauges.
4. The Cycling Switch:
* This is a pressure switch that protects the compressor from damage by preventing it from running when the pressure is too low or too high. A faulty cycling switch can prevent the clutch from engaging.
5. The AC Control System:
* Electrical Connections: Inspect all wiring and connectors related to the AC system, paying close attention to the connector going to the clutch. Look for corrosion, loose connections, or broken wires.
* Relays: The AC system likely uses a relay. Check this relay for proper operation.
6. The Low Pressure Switch:
* This switch cuts power to the compressor clutch to protect it if the refrigerant pressure gets too low. A faulty switch, either stuck open or closed, can be the culprit.
In short, diagnosing the problem yourself requires some basic electrical and mechanical skills, as well as potentially some specialized AC tools. If you're not comfortable working on automotive AC systems, it's best to take your Aerostar to a qualified mechanic or auto AC specialist. Improper handling of refrigerant can be dangerous.
Before you start, remember to disconnect the negative battery terminal to prevent accidental shorts. Always wear safety glasses when working under the hood.
