Thermo Control Amplifier
The thermo control amplifier disconnects the magnet clutch circuit to prevent the evaporator from becoming frosted when the temperature of the evaporator fin drops close to "30°C (37°F)". As the evaporator is cooled, the thermistor (located on the evaporator fin) interrupts the "base" current of the amplifier. This in turn de-energizes the A/C relay coil, which in turn disconnects the magnet clutch circuit.