Expansion valve

How you know it is this

• Cooling that works briefly then fades
• Ice or heavy frost on the pipe at the bulkhead
• Cooling that works at speed but not at idle, or the reverse
• Pressures that read wrong on the gauges in a system with the correct charge

Worth knowing before you buy

• A partly blocked valve gives intermittent cooling that is very easily blamed on a leak. Gauge readings settle it.
• It is the first thing to clog when a compressor has shed debris, which is why it is replaced after any compressor failure.
• Usually at the bulkhead behind the engine, so access is moderate — but on some cars it is behind the dashboard with the evaporator.

Rest of the refrigerant circuit

• A/C compressor
• A/C compressor clutch and coil
• Condenser
• Receiver drier / accumulator
• A/C pipes and hoses
• Pressure switches and sensors
• Evaporator
• Refrigerant and oil