THERMO Control Amplifier
WARNING: This page is about a different car, the 2001 Subaru Impreza and 2000 Subaru Impreza. However, it is still accessible from the selected car via links, so may be relevant.
When temperature of evaporator fins drops close to 36°F (2°C), the thermo control amplifier disconnects A/C compressor clutch circuit to prevent evaporator freeze up. As evaporator is cooled, thermistor (located on evaporator fins) interrupts the base current of thermo control amplifier. This de-energizes A/C relay coil, which disconnects A/C compressor clutch circuit.